Gunicorn works better if temporary folder uses tmpfs (#9534)

This is discussed in the documentation of gunicorn.
You can find more information here: https://docs.gunicorn.org/en/stable/faq.html#how-do-i-avoid-gunicorn-excessively-blocking-in-os-fchmod

Since we are using docker, we always have shared memory
available (at least 64MB).

Closes #9379

Dockerfile

@@ -348,6 +348,7 @@ RUN chmod a+x /entrypoint /clean-logs
 USER airflow
 
 ENV PATH="/home/airflow/.local/bin:${PATH}"
+ENV GUNICORN_CMD_ARGS="--worker-tmp-dir /dev/shm"
 
 WORKDIR ${AIRFLOW_HOME}