Bump rubocop-govuk from 4.14.0 to 4.15.0 #2491

Job	Run time
test-ruby-matrix (4, 0)	2m 34s
test-ruby-matrix (4, 1)	3m 36s
test-ruby-matrix (4, 2)	2m 53s
test-ruby-matrix (4, 3)	1m 41s
CodeQL SAST scan / Analyze	1m 21s
Dependency Review scan / dependency-review-pr	7s
SNYK security analysis / sast	13s
SNYK security analysis / sca	10s
Dependency Review scan / dependency-review-push	0s
Security Analysis / Run Brakeman	15s
Lint JavaScript / Run Standardx	10s
Lint Ruby / Run RuboCop	19s
Test JavaScript / Run Jasmine	38s
Lint SCSS / Run Stylelint	11s
Test Ruby	1s
	14m 9s

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