Fix regex for 0000-NA filenames

[jacobbieker]

Pull Request

Description

The regex for getting the datetime from the filename breaks when there is a filename like:
MSG4-SEVI-MSG15-0000-NA-20230814075918.739000000Z-NA
where the 0100-NA string in most RSS imagery is replaced by 0000-NA. This fixes that

Fixes #

How Has This Been Tested?

• Yes

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked my code and corrected any misspellings

[peterdudfield]

Nice, if the test pass then merge away - thanks for this

[codecov]

Codecov Report

Merging #187 (05b4ef3) into main (4c4458c) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #187   +/-   ##
=======================================
  Coverage   62.37%   62.37%           
=======================================
  Files          10       10           
  Lines        1079     1079           
=======================================
  Hits          673      673           
  Misses        406      406           

Files Changed	Coverage Δ
satip/__init__.py	100.00% <100.00%> (ø)
satip/eumetsat.py	73.46% <100.00%> (-3.27%)	⬇️

... and 1 file with indirect coverage changes

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