Adjust /etc/shadow permissions to unbreak sudo un some setups

In this Ubuntu 24.04 with podman 4.9.3, this was observed:

 + sudo dnf config-manager --enable crb
 sudo: PAM account management error: Authentication service cannot retrieve authentication info
 sudo: a password is required

We're not sure of the exact reason this setup exhibits this problem,
or why it does not with `xcp-ng/xcp-ng-build-env:8.3` which has the same
000 permissions on /etc/shadow, but changing the permissions does avoid
the problem there.

Signed-off-by: Yann Dirson <yann.dirson@vates.tech>
Co-authored-by: Yann Sionneau <yann.sionneau@vates.tech>

Author: ydirson

Dockerfile-9.x

@@ -52,6 +52,9 @@ RUN     dnf install -y \
 # enable repositories commonly required to build
 RUN     dnf config-manager --enable crb
 
+# workaround sudo not working (e.g. in podman 4.9.3 in Ubuntu 24.04)
+RUN     chmod 0400 /etc/shadow
+
 # Set up the builder user
 RUN     bash -c ' \
             OPTS=(); \