Add user timezone setting to test fixtures

Without this change, some tests will fail because the default setting value
for the timezone will override (UTC) when "US/Eastern" is expected.

babybuddy/fixtures/tests.json

@@ -1,4 +1,14 @@
 [
+  {
+    "model": "babybuddy.settings",
+    "pk": 1,
+    "fields": {
+      "user": 1,
+      "dashboard_refresh_rate": "00:01:00",
+      "language": "en",
+      "timezone": "US/Eastern"
+    }
+  },
   {
     "model": "core.child",
     "pk": 1,