Add djangorestframework 3.16 to the test matrix.

Author: tim-schilling

.github/workflows/testing.yml

@@ -32,7 +32,7 @@ jobs:
       matrix:
         python-version: [ "3.9", "3.10", "3.11", "3.12", "3.13"]
         django-version: [ "4.2", "5.0", "5.1", "5.2"]
-        drf-version: ["3.14", "3.15"]
+        drf-version: ["3.14", "3.15", "3.16"]
         exclude:
           # Python 3.9 is incompatible with Django v5+
           - django-version: 5.0