osx-elcapitan - gcloud source repos で複製されたリポジトリを使用すると、credential-gcloud.sh が見つかりません

Question

Mac OS X 10.11 (El Capitan) で、クローンされた GitHub Desktop のリポジトリを同期するとgcloud source repos clone <repository>、次のエラーが表示されます。

git: 'credential-gcloud.sh' is not a git command. See 'git --help'.
2016-08-04 07:44:06.598 GitHub Desktop Login[809:15686] AskPass with arguments: (
    "/Applications/GitHub Desktop.app/Contents/MacOS/GitHub Desktop Login",
    "Username for 'https://source.developers.google.com': "
)
2016-08-04 07:44:06.645 GitHub Desktop Login[809:15686] Error getting keychain item for source.developers.google.com: The specified item could not be found in the keychain.
error: unable to read askpass response from '/Applications/GitHub Desktop.app/Contents/MacOS/GitHub Desktop Login'
fatal: could not read Username for 'https://source.developers.google.com': Device not configured
 (128)