Add missing Sender field in RepositoryVulnerabilityAlertEvent

[ldez]

Reference: https://docs.github.com/en/developers/webhooks-and-events/webhooks/webhook-events-and-payloads#repository_vulnerability_alert

[codecov]

Codecov Report

Merging #2365 (c7e0031) into master (8947206) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2365   +/-   ##
=======================================
  Coverage   98.05%   98.05%           
=======================================
  Files         119      119           
  Lines       10503    10503           
=======================================
  Hits        10299    10299           
  Misses        140      140           
  Partials       64       64           

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

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[gmlewis]

Thank you, @ldez !
LGTM.
Merging.