Create dependabot.yml and update action versions

[abhro]

Dependabot config file from https://discourse.julialang.org/t/psa-use-dependabot-to-update-github-actions-automatically/96001

[abhro]

Gentle bump

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.52%. Comparing base (147f522) to head (780d731).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #31      +/-   ##
==========================================
- Coverage   95.77%   94.52%   -1.26%     
==========================================
  Files           1        1              
  Lines          71       73       +2     
==========================================
+ Hits           68       69       +1     
- Misses          3        4       +1     

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[rfourquet]

LGTM, thanks!
Failures are expected on nightly, codecov failure I'm not sure, and weird failure on mac for v1.4 which looks totally unrelated.