Update sphinx version (#6415)

* Use the current Sphinx version 7.x
* Change language to `en` for Sphinx
* Update sphinx config name `master_doc` -> `root_doc`
  Ref: https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-master_doc
* Remove package pinning workarounds introduced for #6400.
  Also remove an old pinning of the Jinja2 package which
  is unlikely to be still necessary.

Fixes #6400
---------

Co-authored-by: Pavol Juhas <juhas@google.com>

rtd_docs/conf.py

@@ -24,7 +24,7 @@
 # -- Project information -----------------------------------------------------
 
 project = 'Cirq'
-copyright = '2018-2020, The Cirq Developers'  # pylint: disable=redefined-builtin
+copyright = '2018-2024, The Cirq Developers'  # pylint: disable=redefined-builtin
 author = 'The Cirq Developers'
 
 # The short X.Y version
@@ -51,14 +51,14 @@
 source_suffix = {'.rst': 'restructuredtext', '.md': 'markdown'}
 
 # The main toctree document.
-master_doc = 'index'
+root_doc = 'index'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = 'en'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.

rtd_docs/requirements.txt

@@ -1,16 +1,5 @@
 # For generating documentation.
-
-# TODO(#6400,juhas) - upgrade Sphinx and remove the package pins below -------
-alabaster<=0.7.13
-sphinxcontrib-applehelp<=1.0.7
-sphinxcontrib-devhelp<=1.0.5
-sphinxcontrib-htmlhelp<=2.0.4
-sphinxcontrib-qthelp<=1.0.6
-sphinxcontrib-serializinghtml<=1.1.9
-# End of TODO ----------------------------------------------------------------
-
 myst-parser
-Sphinx~=3.2.0
+Sphinx==7.*
 sphinx_rtd_theme
 sphinx-notfound-page
-Jinja2<=3.0.3