Use `tool` rather than hard-coded `"git"`
Use `tool` rather than hard-coded `"git"`

`checkRefFormat` launches a git process using a hard-coded executable name, but a public var `tool` with the same value is declared only a few lines above. It seems like the intent was to use that variable to specify the git executable.
JGiola/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,sschiau/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,sschiau/swift-package-manager,apple/swift-package-manager,sschiau/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,JGiola/swift-package-manager,apple/swift-package-manager,sschiau/swift-package-manager,sschiau/swift-package-manager,apple/swift-package-manager