Fix hardcoded amd64 arch for git-shim #20884

Job	Run time
ci (bundler, bundler1, bundler)	4m 54s
ci (bundler, bundler2, bundler)	4m 42s
ci (cargo, cargo, cargo)	2m 38s
Lint	48s
ci (common, common, common)	2m 2s
ci (composer, composer, composer)	7m 19s
Updater	3m 36s
ci (docker, docker, docker)	2m 17s
ci (elm, elm, elm)	1m 48s
ci (git_submodules, git_submodules, gitsubmodule)	1m 59s
ci (github_actions, github_actions, github-actions)	1m 48s
integration	3m 35s
ci (go_modules, go_module, gomod)	6m 21s
ci (gradle, gradle, gradle)	1m 53s
ci (hex, hex, mix)	5m 36s
ci (maven, maven, maven)	1m 47s
ci (npm_and_yarn, npm_and_yarn, npm)	8m 45s
ci (nuget, nuget, nuget)	11m 35s
ci (pub, pub, pub)	6m 36s
ci (python, python, pip)	7m 49s
ci (python, python_slow, pip)	4m 0s
ci (swift, swift, swift)	7m 30s
ci (devcontainers, devcontainers, devcontainers)	2m 48s
ci (terraform, terraform, terraform)	3m 42s
	1h 45m 48s

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