build

merged_tree: remove `TreeDiffEntry::source` #13520

Job	Run time
Check formatting	17s
Build jj-lib without Git support	42s
cargo-deny (advisories)	22s
build (ubuntu-latest)	4m 31s
cargo-deny (bans licenses sources)	23s
Check protos	44s
build (macos-13)	5m 2s
Clippy check	2m 26s
Check that MkDocs can build the docs	28s
build (macos-14)	3m 59s
build (windows-latest)	8m 28s
Check that MkDocs can build the docs with Poetry 1.8	26s
build (ubuntu-latest, --all-features)	5m 28s
	33m 16s

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