Add asgiref dep to starlette tox envs

The starlette test imports asgiref.testing, which is normally available
as a Django transitive dependency. Since the starlette-specific tox envs
don't install Django, asgiref must be listed explicitly.

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

Author: mitchh456

tox.ini

@@ -54,7 +54,9 @@ deps =
     sqlalchemy
     !starlette036-!starlette10: starlette
     starlette036: starlette>=0.36,<0.37
+    starlette036: asgiref
     starlette10: starlette>=1.0,<1.1
+    starlette10: asgiref
     webtest
 commands =
     pytest {posargs}