Test that ConfigParser treats empty quotes as an empty value

The ConfigParser has supported this for a long time, but it is now
done redundantly since gitpython-developers#2035. This adds a test for it, both to make
clearer that it is intended to work and to allow verifying that it
continues to hold once the legacy special-casing for it is removed.

Author: EliahKagan

test/fixtures/git_config_with_empty_quotes

@@ -0,0 +1,2 @@
+[core]
+  filemode = ""

test/test_config.py

@@ -416,6 +416,10 @@ def test_config_with_quotes(self):
         self.assertEqual(cr.get("user", "name"), "Cody Veal")
         self.assertEqual(cr.get("user", "email"), "[email protected]")
 
+    def test_config_with_empty_quotes(self):
+        cr = GitConfigParser(fixture_path("git_config_with_empty_quotes", read_only=True))
+        self.assertEqual(cr.get("core", "filemode"), "", "quotes can form a literal empty string as value")
+
     def test_config_with_quotes_with_literal_whitespace(self):
         cr = GitConfigParser(fixture_path("git_config_with_quotes_whitespace_inside"), read_only=True)
         self.assertEqual(cr.get("core", "commentString"), "# ")