Update XBeam version to include compiler optimisation

[ben-l-p]

Updated XBeam to change compile flags used in GFortran. The -ftree-parallelize-loops=4 optimisation flag was found to make the beam solver take considerably longer to run than without it. The -ofast flag was added as this should increase performance in some cases with no noticeable impact on results.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b938c5f) 67.69% compared to head (5cc72d7) 67.70%.
Report is 48 commits behind head on develop.

❗ Current head 5cc72d7 differs from pull request most recent head 5a92f77. Consider uploading reports for the commit 5a92f77 to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #272   +/-   ##
========================================
  Coverage    67.69%   67.70%           
========================================
  Files          166      166           
  Lines        26709    26710    +1     
========================================
+ Hits         18081    18083    +2     
+ Misses        8628     8627    -1     

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[sduess]

Hey Ben! Thanks a lot for spotting and speeding up the code.