Throw warning if `CHANGELOG.md` file has not been modified #4967

Job	Run time
no-std (stable, wasm32-unknown-unknown)	1m 29s
Check Rust stable on ubuntu with --all-targets --no-default-features	1m 10s
Clippy	1m 22s
no-std (nightly, wasm32-unknown-unknown)	1m 30s
Check Rust stable on ubuntu with --all-targets	1m 23s
rustfmt	15s
Check Rust stable on ubuntu with --all-targets --all-features	1m 20s
Check Rust nightly on ubuntu with --all-targets --no-default-features	1m 13s
Test Rust stable on ubuntu with --profile test-release	10m 22s
Test Rust nightly on windows-2022	0s
Test Rust stable on ubuntu with --profile test-release --doc	6m 2s
Check Rust nightly on ubuntu with --all-targets	1m 13s
Test Rust nightly on ubuntu with --profile test-release	11m 21s
Check Rust nightly on ubuntu with --all-targets --all-features	1m 14s
Test Rust nightly on ubuntu with --profile test-release --doc	6m 21s
	46m 15s

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