SESSION_BUSY error during sync calls

[makhalin]

Sometimes we get this error message:

status: SESSION_BUSY
issues {
  message: "Pending previous query completion"
  severity: 1
}

We don't use async calls. We just use the context manager `session.checkout', get the response and exit the manager.

It may be necessary to reset the session due to some errors (e.g., issues.Timeout).

ydb-python-sdk/ydb/table.py

Lines 2600 to 2602 in f4fc8eb

	def __exit__(self, exc_type, exc_val, exc_tb):
	if self._acquired is not None:
	self._pool.release(self._acquired)

[GoncharovArtyom]

Problem occurs after using explain query and releasing session after it