gh-140870: Full coverage for _pyrepl._module_completer

[loic-simon]

(split from #140871 as recommanded by @tomasr8)

Add a few tests to get the coverage rate of _pyrepl._module_completer to ~100%:

% python -m coverage run --branch --source=_pyrepl._module_completer -m unittest Lib/test/test_pyrepl/test_pyrepl.py
.....................................s..................................................
----------------------------------------------------------------------
Ran 88 tests in 2.369s

OK (skipped=1)

% python -m coverage report --show-missing
Name                               Stmts   Miss Branch BrPart  Cover   Missing
------------------------------------------------------------------------------
Lib/_pyrepl/_module_completer.py     267      1    104      1    99%   19
------------------------------------------------------------------------------
TOTAL                                267      1    104      1    99%

The only statement left is the import under if TYPE_CHECKING, as expected.

• Issue: PyREPL: auto-complete module attributes in import statements #140870

[tomasr8]

Looks good, thanks! The All required checks pass failed for some reason so I'm just gonna merge main to trigger a new run..

[miss-islington-app]

Thanks @loic-simon for the PR, and @tomasr8 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-143260 is a backport of this pull request to the 3.14 branch.