CI: update test cases with more date parsing cases

[ni4]

As title says.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.05%. Comparing base (7724682) to head (b601d5c). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2275 +/- ## ========================================== + Coverage 84.02% 84.05% +0.03% ========================================== Files 114 114 Lines 23062 23062 ========================================== + Hits 19377 19384 +7 + Misses 3685 3678 -7 ``` | [Flag](https://app.codecov.io/gh/rnpgp/rnp/pull/2275/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/rnpgp/rnp/pull/2275/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp) | `84.05% <ø> (+0.03%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp#carryforward-flags-in-the-pull-request-comment) to find out more.

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[ni4]

Thanks, merging with 2 approvals.