Add Workflow and WorkflowRun to WorkflowRunEvent

[gmlewis]

Fixes #1839.

[gmlewis]

@jacobfoard - PTAL.

[codecov]

Codecov Report

Merging #1840 (68533e9) into master (859ff4c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1840   +/-   ##
=======================================
  Coverage   97.56%   97.56%           
=======================================
  Files         104      104           
  Lines        6602     6602           
=======================================
  Hits         6441     6441           
  Misses         87       87           
  Partials       74       74           

Impacted Files	Coverage Δ
github/event_types.go	100.00% <ø> (ø)

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[jacobfoard]

👍 Looks good to me. Thanks again!