fix: Complete CMake FetchContent implementation #253

Job	Run time
cli-integration (ubuntu)	18s
cli-integration (macos)	3m 54s
cli-integration (windows)	55s
updater-create-pr / cancel-previous-run	4s
updater-create-pr / validate-inputs	9s
updater-test-args / validate-inputs	8s
updater-test-args / cancel-previous-run	3s
updater-create-pr / update	26s
updater-test-args / update	13s
updater-test-outputs	3s
	6m 13s

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