fa952acdb6 ci: Skip read-write of default env vars (MarcoFalke)
Pull request description:
If they remain unset, they use the default anyway. Except for `USER`, but this seems unused anyway.
Can be checked via:
```
sh-5.2# touch /tmp/empty_env
sh-5.2# podman run --rm --env-file /tmp/empty_env 'ubuntu:24.04' env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
container=podman
HOME=/root
HOSTNAME=19ece5c9e052
ACKs for top commit:
0xB10C:
ACK fa952acdb6
Prabhat1308:
utACK [fa952ac](fa952acdb6)
Tree-SHA512: fe0c173b23cfda3025306303a44ffe32ecc57c2e0e1a2376594696f9887ed22f5105da84e898e790041bf15a4aa42a365fba016710ad269d439dda691977be90