Add additional ACSPO reader file patterns

[djhoese]

New versions of the ACSPO files can have new filenames where "SSTskin" was replaced with "SSTsubskin". This PR also changes the unittest-based test class to a pytest one so that I could do parametrize tests.

• Tests added

[codecov]

Codecov Report

Merging #1824 (4d2b1e5) into main (bc23a0d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1824   +/-   ##
=======================================
  Coverage   93.02%   93.02%           
=======================================
  Files         268      268           
  Lines       39576    39577    +1     
=======================================
+ Hits        36816    36817    +1     
  Misses       2760     2760           

Flag	Coverage Δ
behaviourtests	4.72% <0.00%> (-0.01%)	⬇️
unittests	93.60% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
satpy/tests/reader_tests/test_acspo.py	100.00% <100.00%> (ø)

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[coveralls]

Coverage increased (+0.0002%) to 93.542% when pulling 4d2b1e5 on djhoese:feature-new-acspo-names into bc23a0d on pytroll:main.

[mraspaud]

LGTM