Bump govuk_app_config from 9.15.0 to 9.15.1 #3822

Job	Run time
test-ruby-matrix (4, 0)	3m 38s
test-ruby-matrix (4, 1)	3m 2s
test-ruby-matrix (4, 2)	4m 23s
test-ruby-matrix (4, 3)	2m 3s
CodeQL SAST scan / Analyze	2m 12s
Dependency Review scan / dependency-review-pr	22s
Lint JavaScript / Run Standardx	13s
Lint Ruby / Run RuboCop	27s
Dependency Review scan / dependency-review-push	0s
Lint SCSS / Run Stylelint	10s
Security Analysis / Run Brakeman	32s
Test JavaScript / Run Jasmine	1m 24s
Test Ruby	1s
	18m 27s

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