gh-119102: Fix error being thrown on quit when REPL has TERM=dumb

[eugenetriguba]

This fixes the issue where an InvalidTerminal error is being thrown when TERM is set to dumb.

(venv)  src/cpython (gh-119102) % ./python.exe
Python 3.14.0a0 (heads/main-dirty:ab4263a82a, May 21 2024, 11:15:42) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> exit
(venv)  src/cpython (gh-119102) % TERM=dumb ./python.exe
Python 3.14.0a0 (heads/main-dirty:ab4263a82a, May 21 2024, 11:15:42) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
warning: can't use pyrepl: terminal doesn't have the required clear capability
>>> quit()
(venv)  src/cpython (gh-119102) %

On the main branch, we have the following behavior:

(venv)  src/cpython (main) % TERM=dumb ./python.exe
Python 3.14.0a0 (heads/main-dirty:ab4263a82a, May 21 2024, 11:15:42) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
warning: can't use pyrepl: terminal doesn't have the required clear capability
>>> quit()
Exception ignored in atexit callback <function register_readline.<locals>.write_history at 0x103b57a10>:
Traceback (most recent call last):
  File "/Users/eugene/src/cpython/Lib/site.py", line 531, in write_history
    _pyrepl.readline.write_history_file(history)
  File "/Users/eugene/src/cpython/Lib/_pyrepl/readline.py", line 364, in write_history_file
    history = self.get_reader().get_trimmed_history(maxlength)
  File "/Users/eugene/src/cpython/Lib/_pyrepl/readline.py", line 280, in get_reader
    console = UnixConsole(self.f_in, self.f_out, encoding=ENCODING)
  File "/Users/eugene/src/cpython/Lib/_pyrepl/unix_console.py", line 180, in __init__
    self._clear = _my_getstr("clear")
  File "/Users/eugene/src/cpython/Lib/_pyrepl/unix_console.py", line 173, in _my_getstr
    raise InvalidTerminal(
_pyrepl.unix_console.InvalidTerminal: terminal doesn't have the required clear capability

TODO: The test needs a little bit of tweaking still.