Fix xfce4-terminal dependency

[niqdev]

xfce4-terminal is currently failing to open due to the following error

Failed to execute child process "ash" Failed to fdwalk: Operation not permitted

Temporary solution: run the container with --security-opt seccomp=unconfined

Note that the alpine package is still on version 0.8.10 (released +1 year ago) and the current version is 0.9.2 (released 4 days ago). Consider building packages from sources!

Reference

• https://gitlab.xfce.org/apps/xfce4-terminal/-/issues/116
• https://git.alpinelinux.org/aports/tree/community/xfce4-terminal/APKBUILD
• mviereck/x11docker#346