fix: Re-add httpcore[asyncio] to tox.ini and fix renamed import

tox.ini needs httpcore[asyncio] in common/linters/mypy deps until it
can be regenerated from the template. Also fix the test import that
still used the old ASYNC_TRANSPORT_ENABLED name.

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

Author: BYK

tests/integrations/asyncio/test_asyncio.py

@@ -645,9 +645,9 @@ def test_loop_close_patching(sentry_init):
 
 @minimum_python_38
 def test_loop_close_flushes_async_transport(sentry_init):
-    from sentry_sdk.transport import ASYNC_TRANSPORT_ENABLED, AsyncHttpTransport
+    from sentry_sdk.transport import ASYNC_TRANSPORT_AVAILABLE, AsyncHttpTransport
 
-    if not ASYNC_TRANSPORT_ENABLED:
+    if not ASYNC_TRANSPORT_AVAILABLE:
         pytest.skip("httpcore[asyncio] not installed")
 
     sentry_init(integrations=[AsyncioIntegration()])

tox.ini

@@ -384,14 +384,17 @@ deps =
 
     linters: -r requirements-linting.txt
     linters: werkzeug<2.3.0
+    linters: httpcore[asyncio]
 
     mypy: -r requirements-linting.txt
     mypy: werkzeug<2.3.0
+    mypy: httpcore[asyncio]
     ruff: -r requirements-linting.txt
 
     # === Common ===
     py3.8-common: hypothesis
     common: pytest-asyncio
+    common: httpcore[asyncio]
     # See https://github.com/pytest-dev/pytest/issues/9621
     # and https://github.com/pytest-dev/pytest-forked/issues/67
     # for justification of the upper bound on pytest