Rescaling of header pixel size not working

[stephen-riggs]

This caused some errors as the file is opened read-only then we try and change the header. I don't think this is needed anyway as we run the image handler with --force-header-angpix

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.66%. Comparing base (a186050) to head (ca6e0b7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #859   +/-   ##
=======================================
  Coverage   54.65%   54.66%           
=======================================
  Files         104      104           
  Lines       11160    11158    -2     
  Branches     1475     1475           
=======================================
  Hits         6099     6099           
+ Misses       4741     4739    -2     
  Partials      320      320           

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