Create dependabot.yml and update action versions

[abhro]

From https://discourse.julialang.org/t/psa-use-dependabot-to-update-github-actions-automatically/96001

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (f14f023) to head (0cd8080).
Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #30   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          232       232           
=========================================
  Hits           232       232           

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