Update input_output.py

[SeaCelo]

Added a backup source for the SAM in a GH repository

This adds a fallback source for the SAM if the WIDER site is down. Solves #72

cc: @GuBenda

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 56.43%. Comparing base (6e576ae) to head (0a58d9e).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
ogzaf/input_output.py	60.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #73      +/-   ##
==========================================
+ Coverage   56.40%   56.43%   +0.02%     
==========================================
  Files          12       12              
  Lines         367      381      +14     
==========================================
+ Hits          207      215       +8     
- Misses        160      166       +6     

Flag	Coverage Δ
unittests	56.43% <60.00%> (+0.02%)	⬆️

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[jdebacker]

Thanks for this update! I also like the new repo to cache the SAM files in.