Filter out non-editable apache-airflow from constraints. (#25847)

The constraint files should not contain apache-airflow. So far
apache-airflow has been automatically filtered out by the fact that it
has been an editable installation and we filtered out all editable
and file installations from `pip freeze`.

However as of ~12 August 2022, likely setuptools change triggered
a slight behaviour change when `eager-upgrade` installation of
providers from PyPi was run in the CI image. Previously airflow
remained an editable install, but as of 12th of August, such an
installation causes removal of editable airlfow install and
reinstalls it in non-editable mode. While this change is somewhat
confusing, we have to protect against it and remove apache-airflow
from `pip freeze` also in non-editable mode.

(cherry picked from commit cdbad44)

scripts/in_container/run_generate_constraints.sh

@@ -102,6 +102,7 @@ echo
 
 pip freeze | sort | \
     grep -v "apache_airflow" | \
+    grep -v "apache-airflow==" | \
     grep -v "@" | \
     grep -v "/opt/airflow" >>"${CURRENT_CONSTRAINT_FILE}"