Correct Unexpected floats when reading LI L2 LFL

[ClementLaplace]

Makes sure that the method apply_fill_value is not applied when _FillaValue is not into the attributes. It is fixing the bug mentioned there #2854 .

• Closes Unexpected floats when reading LI L2 LFL data #2854

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.11%. Comparing base (01237e2) to head (f06d07e).
Report is 53 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2998      +/-   ##
==========================================
- Coverage   96.11%   96.11%   -0.01%     
==========================================
  Files         383      383              
  Lines       55673    55679       +6     
==========================================
+ Hits        53511    53514       +3     
- Misses       2162     2165       +3     

Flag	Coverage Δ
behaviourtests	3.89% <0.00%> (-0.01%)	⬇️
unittests	96.20% <100.00%> (-0.01%)	⬇️

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[coveralls]

Pull Request Test Coverage Report for Build 12991062112

Details

• 22 of 22 (100.0%) changed or added relevant lines in 4 files are covered.
• 3 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.005%) to 96.217%

---

Files with Coverage Reduction	New Missed Lines	%
satpy/tests/reader_tests/_li_test_utils.py	1	98.55%
satpy/readers/li_base_nc.py	1	99.62%
satpy/tests/reader_tests/test_li_l2_nc.py	1	99.53%

Totals
Change from base Build 12905542942:	-0.005%
Covered Lines:	53761
Relevant Lines:	55875

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💛 - Coveralls

[ameraner]

Thanks for the investigations! I left some comments in the code.

I am also wondering if we still also need the fix for the float64 upcasting when multiplying with the scale_factor, as discussed in the issue...

[ameraner]

Thanks for the fix and the extra more comprehensive tests! Just two things inline.

[ameraner]

LGTM, thanks!

[pnuu]

One suggestion inline.

Maybe we should start splitting the long test helpers to smaller chunks at some point?

I also restarted the one windows CI run.