[dak/master] test_srcformats.py: restore `import unittest`

[Ansgar Burchardt <ansgar@debian.org>]

This was included in fe8fc1bfe57b906e68c7ebc2cd1d0d4e67500ace which
was reverted in the previous commit.
---
 tests/test_srcformats.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/test_srcformats.py b/tests/test_srcformats.py
index fa6f3b38..25fafdbb 100644
--- a/tests/test_srcformats.py
+++ b/tests/test_srcformats.py
@@ -123,4 +123,5 @@ class FormatFromStringTestCase(DakTestCase):
         self.assertInvalid('8.4 (hardy)')
 
 if __name__ == '__main__':
+    import unittest
     unittest.main()
-- 
2.11.0