Bump apache-airflow from 2.5.3 to 2.6.3

Bumps [apache-airflow](https://github.com/apache/airflow) from 2.5.3 to 2.6.3.
- [Release notes](https://github.com/apache/airflow/releases)
- [Changelog](https://github.com/apache/airflow/blob/2.6.3/RELEASE_NOTES.rst)
- [Commits](apache/airflow@2.5.3...2.6.3)

---
updated-dependencies:
- dependency-name: apache-airflow
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]