Remove importorskip guard from async test file

haystack 2.27.0 is releasing imminently; the async mixin classes are
now available in the release candidate.

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

Author: SyedShahmeerAli12

integrations/valkey/tests/test_document_store_async.py

@@ -9,9 +9,6 @@
 import pytest
 import pytest_asyncio
 from haystack.dataclasses import ByteStream, Document
-
-pytest.importorskip("haystack.testing.document_store_async")
-
 from haystack.testing.document_store import (
     CountDocumentsByFilterAsyncTest,
     CountUniqueMetadataByFilterAsyncTest,