Fix the urllib compatibility

[tristanlatr]

The CI suddenly failed with error like:

ERROR   -  Could not retrieve intersphinx object.inv from https://docs.python.org/3/objects.inv
Traceback (most recent call last):
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/pydoctor/sphinx.py", line 397, in get
    return self._session.get(url).content
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/requests/sessions.py", line 602, in get
    return self.request("GET", url, **kwargs)
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/requests/sessions.py", line 589, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/requests/sessions.py", line 747, in send
    r.content
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/requests/models.py", line 899, in content
    self._content = b"".join(self.iter_content(CONTENT_CHUNK_SIZE)) or b""
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/requests/models.py", line 816, in generate
    yield from self.raw.stream(chunk_size, decode_content=True)
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/urllib3/response.py", line 935, in stream
    data = self.read(amt=amt, decode_content=decode_content)
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/urllib3/response.py", line 874, in read
    data = self._raw_read(amt)
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/urllib3/response.py", line 809, in _raw_read
    data = self._fp_read(amt) if not fp_closed else b""
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/urllib3/response.py", line 794, in _fp_read
    return self._fp.read(amt) if amt is not None else self._fp.read()
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/cachecontrol/filewrapper.py", line 96, in read
    self._close()
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/cachecontrol/filewrapper.py", line 76, in _close
    self.__callback(result)
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/cachecontrol/controller.py", line 353, in cache_response
    self._cache_set(cache_url, request, response, body, expires_time)
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/cachecontrol/controller.py", line 274, in _cache_set
    self.serializer.dumps(request, response, body),
  File "/home/runner/work/pydoctor/pydoctor/.tox/apidocs/lib/python3.8/site-packages/cachecontrol/serialize.py", line 54, in dumps
    u"strict": response.strict,
AttributeError: 'HTTPResponse' object has no attribute 'strict'

It might be temporary, but GitHub status seem all green....

Last working checks had the following deps:
alabaster==0.7.13,appdirs==1.4.4,astor==0.8.1,attrs==23.1.0,Automat==22.10.0,Babel==2.12.1,beautifulsoup4==4.12.2,bs4==0.0.1,CacheControl==0.12.11,certifi==2022.12.7,charset-normalizer==3.1.0,ConfigArgParse==1.5.3,constantly==15.1.0,coverage==7.2.5,cython-test-exception-raiser==1.0.0,docutils==0.19,exceptiongroup==1.1.1,hyperlink==21.0.0,hypothesis==6.75.1,idna==3.4,imagesize==1.4.1,importlib-metadata==6.6.0,incremental==22.10.0,iniconfig==2.0.0,Jinja2==3.1.2,lockfile==0.12.2,lunr==0.6.2,MarkupSafe==2.1.2,msgpack==1.0.5,packaging==23.1,pip==23.1.2,pluggy==1.0.0,pydoctor @ file:///home/runner/work/pydoctor/pydoctor/.tox/.tmp/package/1/pydoctor-23.4.0.tar.gz#sha256=59ce4ef301773885d9991a1339d4764a1031da060dd50c72adba428f3ee2b210,Pygments==2.15.1,pytest==7.3.1,requests==2.29.0,setuptools==67.7.2,six==1.16.0,snowballstemmer==2.2.0,sortedcontainers==2.4.0,soupsieve==2.4.1,Sphinx==7.0.0,sphinxcontrib-applehelp==1.0.4,sphinxcontrib-devhelp==1.0.2,sphinxcontrib-htmlhelp==2.0.1,sphinxcontrib-jsmath==1.0.1,sphinxcontrib-qthelp==1.0.3,sphinxcontrib-serializinghtml==1.1.5,toml==0.10.2,tomli==2.0.1,Twisted==22.10.0,typing_extensions==4.5.0,urllib3==1.26.15,wheel==0.40.0,zipp==3.15.0,zope.interface==6.0

Now it's

test: alabaster==0.7.13,appdirs==1.4.4,astor==0.8.1,attrs==23.1.0,Automat==22.10.0,Babel==2.12.1,beautifulsoup4==4.12.2,bs4==0.0.1,CacheControl==0.12.11,certifi==2023.5.7,charset-normalizer==3.1.0,ConfigArgParse==1.5.3,constantly==15.1.0,coverage==7.2.5,cython-test-exception-raiser==1.0.0,docutils==0.20.1,exceptiongroup==1.1.1,hyperlink==21.0.0,hypothesis==6.75.3,idna==3.4,imagesize==1.4.1,importlib-metadata==6.6.0,incremental==22.10.0,iniconfig==2.0.0,Jinja2==3.1.2,lockfile==0.12.2,lunr==0.6.2,MarkupSafe==2.1.2,msgpack==1.0.5,packaging==23.1,pip==23.1.2,pluggy==1.0.0,pydoctor @ file:///home/runner/work/pydoctor/pydoctor/.tox/.tmp/package/1/pydoctor-23.4.0.dev0.tar.gz#sha256=fcdfffb5e99ede58b2c1ab23de8ed7e927534f59845d24915a1d9ba73263778d,Pygments==2.15.1,pytest==7.3.1,requests==2.31.0,setuptools==67.7.2,six==1.16.0,snowballstemmer==2.2.0,sortedcontainers==2.4.0,soupsieve==2.4.1,Sphinx==7.0.1,sphinxcontrib-applehelp==1.0.4,sphinxcontrib-devhelp==1.0.2,sphinxcontrib-htmlhelp==2.0.1,sphinxcontrib-jsmath==1.0.1,sphinxcontrib-qthelp==1.0.3,sphinxcontrib-serializinghtml==1.1.5,toml==0.10.2,tomli==2.0.1,Twisted==22.10.0,typing_extensions==4.6.0,urllib3==2.0.2,wheel==0.40.0,zipp==3.15.0,zope.interface==6.0

Will investigate...

[tristanlatr]

It's the new version of urllib3 that's causing these failures. Since it does not support python3.6 anymore, we can only guard against installing it by adding urllib3<2 in our dependency...

We might also want to move away from cachecontrol all together and adopt it's maintenance fork: psf/cachecontrol#300