test: skip retry-threading test when pyarrow absent

test_retry_kwargs_threaded_into_kernel_client patches
KernelDatabricksClient, which requires importing
databricks.sql.backend.kernel.client — that module imports pyarrow at
load. In the no-pyarrow CI tier the patch target can't be resolved
(AttributeError: module '...kernel' has no attribute 'client'), failing
the Unit Tests (non-PyArrow) jobs while the PyArrow jobs passed.

Add pytest.importorskip("pyarrow") to the test (matching the other
kernel tests) so it skips without pyarrow and runs where it's present.
Corrected the stale class docstring (it patches the client directly,
not via a _create_backend stub).

Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

Author: vikrantpuppala

tests/unit/test_session.py

@@ -413,10 +413,15 @@ def test_use_kernel_pat_builds_minimal_access_token_provider(self):
 class TestKernelRetryOptionsThreading:
     """The connector's ``_retry_*`` kwargs must be forwarded into the
     kernel client's ``retry_options`` on the use_kernel path (the kernel
-    owns the retry loop). Stubs ``_create_backend`` so the kernel client
-    is never imported — wheel-independent — and inspects the
-    ``retry_options`` dict session.py builds by patching the kernel
-    client and capturing its call args.
+    owns the retry loop). Captures the kwargs session.py passes by
+    patching ``KernelDatabricksClient`` and inspecting its call args.
+
+    Patching ``KernelDatabricksClient`` requires importing
+    ``databricks.sql.backend.kernel.client``, which imports pyarrow at
+    module load — so this test is skipped when pyarrow is absent (the
+    no-pyarrow CI tier), matching the other kernel tests. The Rust wheel
+    is still faked via sys.modules so the kernel extension itself isn't
+    needed.
     """
 
     PACKAGE = "databricks.sql"
@@ -425,6 +430,11 @@ def test_retry_kwargs_threaded_into_kernel_client(self):
         import sys
         import types
 
+        pytest.importorskip(
+            "pyarrow",
+            reason="kernel client module imports pyarrow at load",
+        )
+
         # The lazy ``from databricks.sql.backend.kernel.client import
         # KernelDatabricksClient`` triggers ``import databricks_sql_kernel``
         # at module load; the unit-test job has no Rust wheel, so inject