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
• Add your name to AUTHORS.md if not there already

[mraspaud]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.93%. Comparing base (3b9c04e) to head (c698e31).
Report is 500 commits behind head on main.

Additional details and impacted files

@@            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	Coverage Δ
behaviourtests	4.04% <0.00%> (-0.05%)	⬇️
unittests	96.03% <100.00%> (-0.03%)	⬇️

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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