Fix file pattern matching in SEVIRI Native reader

[sfinkens]

Match algorithm version in filename instead of using a fixed one.

• Closes SEVIRI L1.5 native reader does not support files not including 0100 in the file name #1608
• Tests added

[codecov]

Codecov Report

Merging #1609 (ce170bd) into master (2286d24) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head ce170bd differs from pull request most recent head 27e76d2. Consider uploading reports for the commit 27e76d2 to get more accurate results

@@           Coverage Diff           @@
##           master    #1609   +/-   ##
=======================================
  Coverage   92.35%   92.35%           
=======================================
  Files         254      254           
  Lines       37409    37422   +13     
=======================================
+ Hits        34548    34561   +13     
  Misses       2861     2861           

Flag	Coverage Δ
behaviourtests	4.78% <0.00%> (-0.01%)	⬇️
unittests	92.49% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
satpy/tests/reader_tests/test_seviri_l1b_native.py	99.43% <100.00%> (+0.02%)	⬆️

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[ameraner]

LGTM, thanks for taking care of this!

[ghost]

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[mraspaud]

LGTM, thanks for the quick fix.