Fix starlette tox envs: run only starlette tests

Starlette-specific tox envs don't install Django (no django factor),
so running the full test suite causes collection errors on Django tests.
Restrict to starlette integration tests only.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mitchh456

tox.ini

@@ -66,4 +66,4 @@ commands =
 
 [testenv:py{310,311,312,313,314}-starlette{036,10}]
 commands =
-    pytest {posargs} --asyncio-mode=auto
+    pytest tests/integration/test_starlette.py {posargs} --asyncio-mode=auto