Add testing deps for mypy

Author: daneah

.github/workflows/packaging.yml

@@ -50,7 +50,7 @@ jobs:
         run: python -m pip install tox
 
       - name: Run mypy
-        run: python -m tox -e typecheck
+        run: tox -e typecheck
 
   test:
     name: Test

pyproject.toml

@@ -225,6 +225,7 @@ commands = [
 
 [tool.tox.env.typecheck]
 deps = [
+    { replace = "ref", of = ["tool", "tox", "env_run_base", "deps"], extend = true },
     "mypy",
     "django-types",
     "types-requests",