add dependabot config

[valeriupredoi]

Description

This will update GHA action versions when updates are available - very useful to have with manual updating being a bit faff.

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

• This pull request has a descriptive title and labels
• This pull request has a minimal description (most was discussed in the issue, but a two-liner description is still desirable)
• Unit tests have been added (if codecov test fails)
• Any changed dependencies have been added or removed correctly (if need be)
• If you are working on the documentation, please ensure the current build passes
• All tests pass

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.55%. Comparing base (8478494) to head (3106039).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #317   +/-   ##
=======================================
  Coverage   93.55%   93.55%           
=======================================
  Files           7        7           
  Lines         667      667           
=======================================
  Hits          624      624           
  Misses         43       43           

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