[1.6.x] Fixed #21457 -- Allowed fixture file name to contain dots

Thanks Keryn Knight for the report.
Backport of 97ac22ebfc from master.

tests/fixtures_regress/fixtures/path.containing.dots.json

@@ -0,0 +1,9 @@
+[
+    {
+        "pk": "1",
+        "model": "fixtures_regress.absolute",
+        "fields": {
+            "name": "Load Absolute Path Test"
+        }
+    }
+]

tests/fixtures_regress/tests.py

@@ -165,6 +165,14 @@ class TestFixtures(TestCase):
             os.chdir(cwd)
         self.assertEqual(Absolute.objects.count(), 1)
 
+    def test_path_containing_dots(self):
+        management.call_command(
+            'loaddata',
+            'path.containing.dots.json',
+            verbosity=0,
+        )
+        self.assertEqual(Absolute.objects.count(), 1)
+
     def test_unknown_format(self):
         """
         Test for ticket #4371 -- Loading data of an unknown format should fail