Fix TestGitBackend.parse_branches() test.

Commit 5f1ebf2 modified git.Backend.parse_branches() method so
that it no longer skipped a branch if it matched self.fallback_branch.
As a result, we need to modify the expected output for the
parse_branches() test.

Fixes #669.
Merge pull request #670 from toffer/issue-669-fix-test-git-backend

Fix TestGitBackend.parse_branches() test.