Add support for EO-SIP AVHRR LAC data

[mraspaud]

This PR fixes a couple of things in the avhrr gaclac reader to accept EO-SIP (ESA) format LAC data

• [ ] Closes #xxxx
• [x] Tests added
• [ ] Fully documented
• [ ] 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 95.92%. Comparing base (45f918e) to head (5ffe15e). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2762 +/- ## ======================================= Coverage 95.92% 95.92% ======================================= Files 377 377 Lines 53468 53489 +21 ======================================= + Hits 51287 51310 +23 + Misses 2181 2179 -2 ``` | [Flag](https://app.codecov.io/gh/pytroll/satpy/pull/2762/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/2762/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `4.10% <0.00%> (-0.01%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/pytroll/satpy/pull/2762/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `96.02% <100.00%> (+<0.01%)` | :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=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

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[coveralls]

Pull Request Test Coverage Report for Build 8348304532

Details

• 25 of 25 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.006%) to 96.005%

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Totals
Change from base Build 8282476634:	0.006%
Covered Lines:	51182
Relevant Lines:	53312

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💛 - Coveralls