[MINOR][TEST][CONNECT][PYTHON] Fix flaky test_client.py test

### What changes were proposed in this pull request?

Fix flaky test_client.py test.
`test_not_found_recovers` is flaky, this can be reproduced by running the test repeatedly, e.g. with
```
seq 10 | xargs -I {} python/run-tests --testnames 'pyspark.sql.tests.connect.client.test_client' --python-executables=python
```
This change fixes the test.

### Why are the changes needed?

Flaky test

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

Test change, ran locally.

### Was this patch authored or co-authored using generative AI tooling?

No

Closes #51368 from khakhlyuk/alex-khakhlyuk_data/fix-flaky-test-client.

Authored-by: Alex Khakhlyuk <alex.khakhlyuk@gmail.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

Author: khakhlyuk

python/pyspark/sql/tests/connect/client/test_client.py

@@ -423,7 +423,7 @@ def not_found():
             def checks():
                 self.assertEqual(2, stub.execute_calls)
                 self.assertEqual(0, stub.attach_calls)
-                self.assertEqual(0, stub.release_calls)
+                self.assertEqual(1, stub.release_calls)
                 self.assertEqual(0, stub.release_until_calls)
 
             eventually(timeout=1, catch_assertions=True)(checks)()