colcontainer: close PDQ during TestPartitionedDiskQueueSimulatedExternal

Close the `PartitionedDiskQueue` at the end of
`TestPartitionedDiskQueueSimulatedExternal/HashJoin`.

Fixes: #106119

Release note: None

pkg/sql/colcontainer/partitionedqueue_test.go

@@ -310,5 +310,8 @@ func TestPartitionedDiskQueueSimulatedExternal(t *testing.T) {
 		}
 
 		joinRepartition(0, 0, numRepartitions, 0)
+
+		require.NoError(t, p.Close(ctx))
+		countingFS.assertOpenFDs(t, sem, 0, 0)
 	})
 }