pygettext: Improve test coverage

Options that should be tested:

• --extract-all (NO-OP, deprecated since 3.14)
• --add-comments
• --default-domain
• --escape
  • https://github.com/python/cpython/pull/131902
  • https://github.com/python/cpython/pull/132244
• --docstrings
• --help
• --keyword
• --no-default-keywords
• --no-location
• --add-location
• --output
  • https://github.com/python/cpython/pull/133041
• --output-dir
• --style stylename
• --verbose
• --version
  • https://github.com/python/cpython/pull/133022
• --width
  • https://github.com/python/cpython/pull/130705
• --exclude-file
  • https://github.com/python/cpython/pull/131381
• --no-docstrings
  • https://github.com/python/cpython/pull/133021 (Renames to exclude-docstrings)

Linked PRs

• gh-130198
• gh-131381
• gh-131902
• gh-132032
• gh-132033
• gh-132244
• gh-133021
• gh-133022
• gh-133041
• gh-133048
• gh-133255
• gh-133266
• gh-133309