use gix_path::env::shell() to get the shell in git2-hooks #9036

Job	Run time
build (ubuntu-latest, 1.70)	2m 15s
build (ubuntu-latest, nightly)	2m 8s
build-linux-musl (nightly)	3m 40s
build-linux-musl (1.70)	3m 33s
build (ubuntu-latest, stable)	2m 14s
build (macos-latest, nightly)	2m 28s
build-apple-x86 (1.70)	1m 53s
build (macos-latest, stable)	2m 32s
build-linux-musl (stable)	3m 15s
build (windows-latest, 1.70)	6m 58s
build-linux-arm (stable)	5m 48s
build (windows-latest, stable)	6m 53s
build-apple-x86 (nightly)	1m 54s
Test Homebrew Formula (macOS)	7m 22s
build (macos-latest, 1.70)	2m 51s
build-linux-arm (1.70)	6m 0s
udeps	2m 19s
build-linux-arm (nightly)	6m 32s
Changelog Test	9s
build (windows-latest, nightly)	7m 9s
Lints	42s
build-apple-x86 (stable)	1m 48s
	1h 20m 23s

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