docs: Add changelog entry for CMake FetchContent support #268

Job	Run time
updater-create-pr / validate-inputs	15s
updater-create-pr / cancel-previous-run	5s
cli-integration (ubuntu)	16s
cli-integration (macos)	4m 20s
updater-test-args / cancel-previous-run	5s
cli-integration (windows)	21s
updater-test-args / validate-inputs	8s
updater-test-args / update	13s
updater-create-pr / update	23s
updater-test-outputs	6s
	6m 12s

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