infra: change dependabot action updates to monthly

[math411]

Issue #, if available:

Description of changes:

Testing done: Changing the keyword from the weekly cycle

Merge Checklist

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General

• [ ] I have read the CONTRIBUTING doc
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• [ ] I have updated any necessary documentation, including READMEs and API docs (if appropriate)

Tests

• [ ] I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (ecbe76d) to head (ea596a9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #951 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 135 135 Lines 8919 8919 Branches 2002 2002 ========================================= Hits 8919 8919 ```

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