Fix SubprocessGitClient on Windows Python3.

dulwich/client.py

@@ -683,6 +683,7 @@ class SubprocessGitClient(TraditionalGitClient):
         if self.git_command is None:
             git_command = find_git_command()
         argv = git_command + [service, path]
+        argv = ['git', service.decode('ascii'), path]
         p = SubprocessWrapper(
             subprocess.Popen(argv, bufsize=0, stdin=subprocess.PIPE,
                              stdout=subprocess.PIPE,