Bump apache-airflow from 2.3.4 to 2.6.0 in /requirements/constraints

Bumps [apache-airflow](https://github.com/apache/airflow) from 2.3.4 to 2.6.0.
- [Release notes](https://github.com/apache/airflow/releases)
- [Changelog](https://github.com/apache/airflow/blob/main/RELEASE_NOTES.rst)
- [Commits](apache/airflow@2.3.4...2.6.0)

---
updated-dependencies:
- dependency-name: apache-airflow
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements/constraints/apache-airflow-2.3.4-constraints-3.9-FIXED.txt

@@ -37,7 +37,7 @@ Werkzeug==2.2.2
 alembic==1.8.1
 amqp==5.1.1
 anyio==3.6.1
-apache-airflow==2.3.4
+apache-airflow==2.6.0
 apispec==3.3.2
 argcomplete==2.0.0
 attrs==22.1.0