Configure Dependabot for GH Actions (#341)

[madhead]

Fixes #341

[codecov-commenter]

Codecov Report

Merging #342 (2000356) into master (8b4452b) will not change coverage.
The diff coverage is n/a.

❗ Current head 2000356 differs from pull request most recent head 4d56ee1. Consider uploading reports for the commit 4d56ee1 to get more accurate results

@@           Coverage Diff           @@
##           master     #342   +/-   ##
=======================================
  Coverage   89.60%   89.60%           
=======================================
  Files          15       15           
  Lines         789      789           
=======================================
  Hits          707      707           
  Misses         70       70           
  Partials       12       12           

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