fix: staticcheck warnings in events/codebuild.go

[shogo82148]

Issue #, if available:

Description of changes:

it fixes the following warnings.

    # events/codebuild.go:18:2: SA9004: only the first constant in this group has an explicit type (staticcheck)
    # 	CodeBuildPhaseStatusFailed     CodeBuildPhaseStatus = "FAILED"
    # 	^
    # events/codebuild.go:31:2: SA9004: only the first constant in this group has an explicit type (staticcheck)
    # 	CodeBuildPhaseTypeSubmitted       CodeBuildPhaseType = "SUBMITTED"
    # 	^

In addition, it fixes that CodeBuildEventDetail.CurrentPhase and CodeBuildEventDetail. CompletedPhase have incorrect type.

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[codecov-commenter]

Codecov Report

Merging #323 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #323   +/-   ##
=======================================
  Coverage   72.46%   72.46%           
=======================================
  Files          18       18           
  Lines         730      730           
=======================================
  Hits          529      529           
  Misses        136      136           
  Partials       65       65           

Impacted Files	Coverage Δ
events/codebuild.go	44.44% <ø> (ø)

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