merge_tools: preserve executable bit on resolve #17264

Job	Run time
Check protos	31s
cargo-deny (advisories)	24s
build (ubuntu-latest)	5m 0s
build (macos-13)	7m 15s
Check that MkDocs can build the docs	11s
cargo-deny (bans licenses sources)	23s
Check formatting	16s
build (macos-14)	3m 57s
build (windows-latest)	9m 21s
Build jj-lib without Git support	45s
Clippy check	2m 40s
build (ubuntu-latest, --all-features)	5m 58s
Check that MkDocs can build the docs with latest Python and uv	15s
	36m 56s

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