deps: update dependency dj-database-url to v3

Author: renovate[bot]

pyproject.toml

@@ -66,7 +66,7 @@ flagsmith-test-tools = "common.test_tools.plugin"
 
 [dependency-groups]
 dev = [
-    "dj-database-url (>=2.3.0, <3.0.0)",
+    "dj-database-url (>=3.1.0, <3.2.0)",
     "django-stubs (>=5.1.3, <6.0.0)",
     "djangorestframework-stubs (>=3.15.3, <4.0.0)",
     "mypy (>=1.15.0, <2.0.0)",