Add scripts\in_container folder when all other sources are removed. (…

…#36129)

This allows to tests the scripts that require --mount-sources remove
but you run some scripts inside the container (for example this
was the case when modifying installation of airflow and
providers to be run in Python in #36094. In order to debug those,
The image needed to be rebuild to run the "in-container" scripts..

More importantly - users will also have to rebuild the image after
they rebase to latest main - in order to use the new scripts when
runinng `--use-airflow-version`.

This change will make the modification coming from main visible in
their images even without rebuilding the image.

scripts/ci/docker-compose/remove-sources.yml

@@ -17,6 +17,13 @@
 ---
 services:
   airflow:
-    # Removes airflow sources from container
     volumes:
-      - ./empty:/opt/airflow/airflow:cached
+      # Removes airflow sources from container
+      - type: bind
+        source: ./empty
+        target: /opt/airflow/airflow:cached
+      # However we keep in_container scripts in order to be able to debug easily the scripts that
+      # are run with --mount-sources removed flag - such as installing airflow and providers
+      - type: bind
+        source: ../../../scripts/in_container
+        target: /opt/airflow/scripts/in_container:cached