fix(airflow): Explicitly install python version, and call python with the version

Also ignore lint warning about pinning pip packages.

Author: NickLarsenNZ

.hadolint.yaml

@@ -10,6 +10,11 @@ ignored:
   # Reason: We use buildx which handles the build graph, no explicit image tags necessary
   - DL3006
 
+  # Warning: Pin versions in pip.
+  # https://github.com/hadolint/hadolint/wiki/DL3006
+  # Reason: So far we haven't pinned versions. If we decide to, we should do that as a separate piece of work.
+  - DL3013
+
   # Warning: Use the -y switch to avoid manual input dnf install -y <package>
   # https://github.com/hadolint/hadolint/wiki/DL3038
   # Reason: We set `assumeyes=True` in dnf.conf in our base image

airflow/Dockerfile

@@ -33,6 +33,7 @@ RUN microdnf update && \
         libpq-devel \
         openldap-devel \
         openssl-devel \
+        python${PYTHON} \
         python${PYTHON}-devel \
         python${PYTHON}-pip \
         python${PYTHON}-wheel \
@@ -41,7 +42,7 @@ RUN microdnf update && \
     microdnf clean all && \
     rm -rf /var/cache/yum
 
-RUN python3 -m venv --system-site-packages /stackable/app && \
+RUN python${PYTHON} -m venv --system-site-packages /stackable/app && \
     source /stackable/app/bin/activate && \
     pip install --no-cache-dir --upgrade pip && \
     pip install --no-cache-dir apache-airflow[${AIRFLOW_EXTRAS}]==${PRODUCT} --constraint /tmp/constraints.txt && \