date: add test_date_allow_missing_year and test_date_allow_spaces_after_month

[Devel08]

this pr will add tests for #14648 and #14649

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Note: The gnu test tests/env/env-signal-handler was skipped on 'main' but is now failing.

[Devel08]

@cakebaker Can we merge that, so I can add references to the tests in the respective issues?

[cakebaker]

Thanks!