cmd/go: TestScript/get_(unicode|dotfiles|brace) failing on Plan 9

[0intro]

TestScript/get_unicode, TestScript/get_dotfiles and TestScript/get_brace are failing on Plan 9 (when git is available in the path), because they expect a full-featured Git command, while on Plan 9, the git tool has been emulated as a simple rc script.

--- FAIL: TestScript/get_unicode (0.01s)
    --- FAIL:  (1.85s)
        script_test.go:183: 
            # Construct a repository that imports a non-ASCII path. (1.657s)
            > cd $WORK/_origin/example.com/unicode
            $WORK/_origin/example.com/unicode
            > exec git init
            [stderr]
            usage: git <command> [<args>]
            [exit status: 'git 1643000: usage']
            FAIL: testdata/script/get_unicode.txt:5: unexpected command failure
            
    --- FAIL: TestScript/get_dotfiles (1.68s)
        script_test.go:183: 
            # Set up a benign repository and a repository with a dotfile name. (1.655s)
            > cd $WORK/_origin/foo
            $WORK/_origin/foo
            > exec git init
            [stderr]
            usage: git <command> [<args>]
            [exit status: 'git 1643038: usage']
            FAIL: testdata/script/get_dotfiles.txt:5: unexpected command failure
            
    --- FAIL: TestScript/get_brace (1.66s)
        script_test.go:183: 
            # Set up some empty repositories. (1.644s)
            > cd $WORK/_origin/foo
            $WORK/_origin/foo
            > exec git init
            [stderr]
            usage: git <command> [<args>]
            [exit status: 'git 1643043: usage']
            FAIL: testdata/script/get_brace.txt:5: unexpected command failure
            
FAIL

[gopherbot]

Change https://golang.org/cl/157119 mentions this issue: cmd/go: skip tests using Git on Plan 9