support FIRG file-patterns coming from EUMETCast-Europe

[fwfichtner]

• [x] Closes #2881
• [ ] Tests added
• [ ] Fully documented
• [x] Add your name to AUTHORS.md if not there already

[codecov[bot]]

Codecov Report

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

Project coverage is 95.97%. Comparing base (6860030) to head (abe48ae). Report is 382 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2882 +/- ## ========================================== - Coverage 95.99% 95.97% -0.02% ========================================== Files 368 368 Lines 53985 53973 -12 ========================================== - Hits 51821 51801 -20 - Misses 2164 2172 +8 ``` | [Flag](https://app.codecov.io/gh/pytroll/satpy/pull/2882/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | Coverage Δ | | |---|---|---| | [behaviourtests](https://app.codecov.io/gh/pytroll/satpy/pull/2882/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `4.02% <ø> (+<0.01%)` | :arrow_up: | | [unittests](https://app.codecov.io/gh/pytroll/satpy/pull/2882/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `96.07% <ø> (-0.02%)` | :arrow_down: | 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=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[coveralls]

Pull Request Test Coverage Report for Build 10365306296

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 8 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.01%) to 96.073%

---

Files with Coverage Reduction	New Missed Lines	%
satpy/tests/utils.py	2	93.16%
satpy/tests/reader_tests/gms/test_gms5_vissr_l1b.py	3	98.67%
satpy/tests/reader_tests/gms/test_gms5_vissr_navigation.py	3	97.18%
<!--	Total:	8		-->

Totals
Change from base Build 10303695673:	-0.01%
Covered Lines:	52030
Relevant Lines:	54157

---

💛 - Coveralls

[ameraner]

LGTM, thanks for adding the path, good to see that it was the only thing needed to support the files!