fix(ci): run security scan on master pushes

[agammann]

Security scan currently filters push events to maser, while the default branch is master. On the f686805 master push, Lint and Tests ran, but Security scan did not. Change the filter to master so future pushes start the security workflow.

Validation: git diff --check passed, and the branch differs from master by this one-line change only.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.87%. Comparing base (f686805) to head (280e528).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1011      +/-   ##
==========================================
+ Coverage   98.85%   98.87%   +0.02%     
==========================================
  Files          32       32              
  Lines        4728     4728              
==========================================
+ Hits         4674     4675       +1     
+ Misses         54       53       -1     

Flag	Coverage Δ
unittests	98.87% <ø> (+0.02%)	⬆️

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