Update Dependabot interval from weekly to monthly

[linw1995]

Change the update schedule for both GitHub Actions and Cargo dependency checks from weekly to monthly intervals to reduce frequency of automated dependency updates.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.34%. Comparing base (c2afbdd) to head (725afc7).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #133      +/-   ##
==========================================
- Coverage   80.38%   80.34%   -0.05%     
==========================================
  Files          13       13              
  Lines        4935     4935              
==========================================
- Hits         3967     3965       -2     
- Misses        968      970       +2     

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