Update the vii_l1b-reader, for new testdata format of VII

[shornqui]

EUMETSAT has updated the EPS-SG testdata for VII (METimage), to version 2.1. There is one variable in the netCDF-file that has changed names. Because of that the VII-level1b-reader needs to be update. (I have also checked with EUMETSAT, this change is meant to stay -the old variable name was a bug.)

There were no need to add new tests, but there was an updated test, due to this change.

• [ ] Closes #xxxx
• [ ] 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 95.93%. Comparing base (3b9c04e) to head (c698e31). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2807 +/- ## ========================================== - Coverage 95.95% 95.93% -0.03% ========================================== Files 379 366 -13 Lines 53888 53528 -360 ========================================== - Hits 51708 51351 -357 + Misses 2180 2177 -3 ``` | [Flag](https://app.codecov.io/gh/pytroll/satpy/pull/2807/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/2807/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `4.04% <0.00%> (-0.05%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/pytroll/satpy/pull/2807/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `96.03% <100.00%> (-0.03%)` | :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.

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[coveralls]

Pull Request Test Coverage Report for Build 9318985608

Details

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.032%

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Totals
Change from base Build 9157044280:	0.0%
Covered Lines:	51580
Relevant Lines:	53711

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💛 - Coveralls