Apache Airflow 2.6.3

## Bug Fixes - Use linear time regular expressions (#32303) - Fix triggerers alive check and add a new conf for triggerer heartbeat rate (#32123) - Catch the exception that triggerer initialization failed (#31999) - Hide sensitive values from extra in connection edit form (#32309) - Sanitize ``DagRun.run_id`` and allow flexibility (#32293) - Add triggerer canceled log (#31757) - Fix try number shown in the task view (#32361) - Retry transactions on occasional deadlocks for rendered fields (#32341) - Fix behaviour of LazyDictWithCache when import fails (#32248) - Remove ``executor_class`` from Job - fixing backfill for custom executors (#32219) - Fix bugged singleton implementation (#32218) - Use ``mapIndex`` to display extra links per mapped task. (#32154) - Ensure that main triggerer thread exits if the async thread fails (#32092) - Use ``re2`` for matching untrusted regex (#32060) - Render list items in rendered fields view (#32042) - Fix hashing of ``dag_dependencies`` in serialized dag (#32037) - Return ``None`` if an XComArg fails to resolve in a multiple_outputs Task (#32027) - Check for DAG ID in query param from url as well as kwargs (#32014) - Flash an error message instead of failure in ``rendered-templates`` when map index is not found (#32011) - Fix ``ExternalTaskSensor`` when there is no task group TIs for the current execution date (#32009) - Fix number param html type in trigger template (#31980, #31946) - Fix masking nested variable fields (#31964) - Fix ``operator_extra_links`` property serialization in mapped tasks (#31904) - Decode old-style nested Xcom value (#31866) - Add a check for trailing slash in webserver base_url (#31833) - Fix connection uri parsing when the host includes a scheme (#31465) - Fix database session closing with ``xcom_pull`` and ``inlets`` (#31128) - Fix DAG's ``on_failure_callback`` is not invoked when task failed during testing dag. (#30965) - Fix airflow module version check when using ``ExternalPythonOperator`` and debug logging level (#30367) ## Misc/Internal - Fix ``task.sensor`` annotation in type stub (#31954) - Limit ``Pydantic`` to ``< 2.0.0`` until we solve ``2.0.0`` incompatibilities (#32312) - Fix ``Pydantic`` 2 pickiness about model definition (#32307) ## Doc only changes - Add explanation about tag creation and cleanup (#32406) - Minor updates to docs (#32369, #32315, #32310, #31794) - Clarify Listener API behavior (#32269) - Add information for users who ask for requirements (#32262) - Add links to DAGRun / DAG / Task in Templates Reference (#32245) - Add comment to warn off a potential wrong fix (#32230) - Add a note that we'll need to restart triggerer to reflect any trigger change (#32140) - Adding missing hyperlink to the tutorial documentation (#32105) - Added difference between Deferrable and Non-Deferrable Operators (#31840) - Add comments explaining need for special "trigger end" log message (#31812) - Documentation update on Plugin updates. (#31781) - Fix SemVer link in security documentation (#32320) - Update security model of Airflow (#32098) - Update references to restructured documentation from Airflow core (#32282) - Separate out advanced logging configuration (#32131) - Add ``™`` to Airflow in prominent places (#31977)