Update dependabot cadence

[slifty]

This PR shifts to monthly dependabot updates + a 7-day cooldown.

There's no issue since we're doing this everywhere.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.24%. Comparing base (6e7d8a6) to head (5cbb236).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #579   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files         102      102           
  Lines        2457     2457           
  Branches      410      410           
=======================================
  Hits         2414     2414           
  Misses         39       39           
  Partials        4        4           

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