Always record the git branch command as success

This is causing the build to be marked as FAILED when the repository
has no branches.

Closes #3644

Author: humitos

readthedocs/vcs_support/backends/git.py

@@ -122,8 +122,8 @@ def parse_tags(self, data):
     @property
     def branches(self):
         # Only show remote branches
-        retcode, stdout, _ = self.run('git', 'branch', '-r')
-        # error (or no tags found)
+        retcode, stdout, _ = self.run('git', 'branch', '-r', record_as_success=True)
+        # error (or no branches found)
         if retcode != 0:
             return []
         return self.parse_branches(stdout)