Schema update action tests

[smashwilson]

This pull request exists to test #2108 by changing the GitHub Action to a trigger-on-push workflow and attempting to artificially trigger different scenarios. It should never be merged.

Scenarios

• Schema up to date - succeed, but do nothing. check run
• Schema update that changes nothing - push a commit with the schema update directly to the originating branch (so, this one). check run
• Schema update that changes one or more compiled queries - open a new pull request containing the updated schema and generated query files. check run | pull request GraphQL schema update #2121
• Schema update that changes compiled queries while a previous pull request is already open - do nothing. check run
• Schema update that breaks compiled queries - open a new pull request containing the updated schema that shows the relay-compiler output in its body. check run | pull request GraphQL schema update #2123

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View rendered actions/schema-up/README.md

[codecov]

Codecov Report

Merging #2116 into master will decrease coverage by 0.44%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #2116      +/-   ##
=========================================
- Coverage   92.65%   92.2%   -0.45%     
=========================================
  Files         207     207              
  Lines       12045   12032      -13     
  Branches     1764    1747      -17     
=========================================
- Hits        11160   11094      -66     
- Misses        885     938      +53

Impacted Files	Coverage Δ
lib/containers/user-mention-tooltip-container.js	0% <0%> (-100%)	⬇️
lib/containers/issueish-tooltip-container.js	14.28% <0%> (-85.72%)	⬇️
lib/shared/keytar-strategy.js	38.75% <0%> (-19.38%)	⬇️
lib/git-temp-dir.js	90.9% <0%> (-9.1%)	⬇️
lib/models/file-system-change-observer.js	88% <0%> (-8%)	⬇️
lib/helpers.js	85.58% <0%> (-4.42%)	⬇️
lib/models/issueish.js	83.33% <0%> (-0.46%)	⬇️
lib/git-shell-out-strategy.js	99.8% <0%> (-0.2%)	⬇️
lib/items/issueish-detail-item.js	98.36% <0%> (-0.03%)	⬇️
lib/views/reviews-view.js	83.23% <0%> (ø)	⬆️
... and 7 more

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