Incompatible with Airflow: 2.2

[Dmytro Kulyk]

After upgrade to Airflow 2.2.x exporter failing to expose metrics
Seems like ORM model needs to be adapted to core changes

Python version: 3.9.7
Airflow version: 2.2.0
Node: airflow-webserver-84659cd4c4-9xtf7
-------------------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 1952, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 1821, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/airflow/.local/lib/python3.9/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow_prometheus_exporter/prometheus_exporter.py", line 492, in list
    return Response(generate_latest(), mimetype='text')
  File "/home/airflow/.local/lib/python3.9/site-packages/prometheus_client/exposition.py", line 177, in generate_latest
    for metric in registry.collect():
  File "/home/airflow/.local/lib/python3.9/site-packages/prometheus_client/registry.py", line 83, in collect
    for metric in collector.collect():
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow_prometheus_exporter/prometheus_exporter.py", line 378, in collect
    for task in get_task_duration_info():
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow_prometheus_exporter/prometheus_exporter.py", line 259, in get_task_duration_info
    session.query(
  File "/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/orm/scoping.py", line 163, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/orm/session.py", line 1589, in query
    return self._query_cls(entities, self, **kwargs)
  File "/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/orm/query.py", line 197, in __init__
    self._set_entities(entities)
  File "/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/orm/query.py", line 223, in _set_entities
    entity_wrapper(self, ent)
  File "/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/orm/query.py", line 4720, in __init__
    raise sa_exc.InvalidRequestError(
sqlalchemy.exc.InvalidRequestError: SQL expression, column, or mapped entity expected - got 'ColumnAssociationProxyInstance(AssociationProxy('dag_run', 'execution_date'))'