cmd/gomote: don't push .git even if it is a file

In `git worktree` checkouts, rather than a .git directory, .git is a
file containing the path of the real repository. Presence of this file
will confuse git invoked by the go tool, so don't push it, just as we
don't push a .git directory.

For golang/go#58218.

Change-Id: I2d316d5672a87ba9cb7175a07e06e99a3392a85d
Reviewed-on: https://go-review.googlesource.com/c/build/+/480635
Reviewed-by: Carlos Amedee <amedee@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Pratt <mpratt@google.com>

Author: prattmic

Diff for: cmd/gomote/push.go

@@ -179,15 +179,21 @@ func doPush(ctx context.Context, name, goroot string, dryRun, detailedProgress b
 		if rel == "." {
 			return nil
 		}
+		if rel == ".git" {
+			if fi.IsDir() {
+				return filepath.SkipDir
+			}
+			return nil // .git is a file in `git worktree` checkouts.
+		}
 		if fi.IsDir() {
 			switch rel {
-			case ".git", "pkg", "bin":
+			case "pkg", "bin":
 				return filepath.SkipDir
 			}
 		}
 		inf := fileInfo{fi: fi}
 		if isGitIgnored(path) {
-			if fi.Mode().IsDir() {
+			if fi.IsDir() {
 				return filepath.SkipDir
 			}
 			return nil