changelog: clarify that commit signing support is partial #9665

Job	Run time
Check that MkDocs can build the docs with Poetry 1.3.2	51s
Check protos	29s
cargo-deny (advisories)	25s
build (ubuntu-latest)	3m 19s
cargo-deny (bans licenses sources)	22s
build (macos-14)	2m 36s
Check formatting	15s
Clippy check	2m 17s
build (windows-latest)	6m 28s
Check that MkDocs can build the docs	24s
build (ubuntu-latest, --all-features)	4m 27s
	21m 53s

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