Throw warning if `CHANGELOG.md` file has not been modified #4968

Job	Run time
Clippy	1m 17s
no-std (stable, wasm32-unknown-unknown)	1m 24s
Check Rust stable on ubuntu with --all-targets --no-default-features	1m 20s
rustfmt	16s
no-std (nightly, wasm32-unknown-unknown)	1m 29s
Check Rust stable on ubuntu with --all-targets	1m 11s
Test Rust stable on ubuntu with --profile test-release	10m 13s
Check Rust stable on ubuntu with --all-targets --all-features	1m 43s
Test Rust nightly on windows-2022	0s
Check Rust nightly on ubuntu with --all-targets --no-default-features	1m 19s
Test Rust stable on ubuntu with --profile test-release --doc	5m 54s
Check Rust nightly on ubuntu with --all-targets	1m 13s
Test Rust nightly on ubuntu with --profile test-release	11m 4s
Check Rust nightly on ubuntu with --all-targets --all-features	1m 21s
Test Rust nightly on ubuntu with --profile test-release --doc	6m 25s
	46m 9s

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