Fix flaky test failure

[suketa]

https://github.com/suketa/ruby-duckdb/actions/runs/10793328758/job/29935003156#step:8:24

  1) Failure:
DuckDBTest::PendingResultTest#test_execute_check_state [test/duckdb_test/pending_result_test.rb:53]:
Expected: :no_tasks
  Actual: :ready

[suketa]

  1) Failure:
DuckDBTest::PendingResultTest#test_state [test/duckdb_test/pending_result_test.rb:21]:
Expected: :ready
  Actual: :no_tasks

  2) Failure:
DuckDBTest::PendingResultTest#test_execute_check_state [test/duckdb_test/pending_result_test.rb:53]:
Expected: :no_tasks
  Actual: :error

[suketa]

fixed by #736

[suketa]

This issue must be fixed like as test_query_progress in test/duckdb_test/connection_test.rb

[suketa]

This issue does not happen recently. I close this issue.