Add missing CreatedAt and UpdatedAt fields to CheckSuite

[recurser]

This adds the created_at and updated_at fields to CheckSuite. See REST API docs.

[codecov]

Codecov Report

Merging #1983 (acf64ed) into master (f47f8fe) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1983   +/-   ##
=======================================
  Coverage   97.84%   97.84%           
=======================================
  Files         105      105           
  Lines        6809     6809           
=======================================
  Hits         6662     6662           
  Misses         80       80           
  Partials       67       67           

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

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[gmlewis]

Thank you, @recurser !
LGTM.
Merging.