ci: Add deployment status check workflow

[peaceiris]

cf. https://github.com/fastai/fastpages/blob/9ca83a401862ef7da0689123c78c0e68a445b983/.github/workflows/gh-page.yaml

[codecov]

Codecov Report

Merging #125 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #125   +/-   ##
=======================================
  Coverage   95.58%   95.58%           
=======================================
  Files           2        2           
  Lines          68       68           
  Branches       14       14           
=======================================
  Hits           65       65           
  Misses          3        3           

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