Bump of our Xfce build container to Ubuntu 22.04 LTS

[Romain Bouvier]

Hello,

Our docker builder for the gitlab CI has been upgraded to Ubuntu 22.04 LTS (from Ubuntu 20.04), to prepare Xfce 4.18, which will needs the following dependencies:

* glib-2.0 >= 2.66 (Same version for gmodule-2.0, gobject-2.0, gthread-2.0, gio-2.0 and gdbus)
* gtk >= 3.24
* libcairo >= 1.16
* gdk-pixbuf-2.0 >= 2.40

See https://wiki.xfce.org/releng/4.18/roadmap#changes_in_dependencies (https://wiki.xfce.org/releng/4.18/roadmap#changes_in_dependencies)

The image bump introduce a regression on some "make distcheck" targets in CI, due to an intltool 'bug' (https://code.launchpad.net/~invidian/intltool/fix-dangling-lock-file/+merge/400825 (https://code.launchpad.net/~invidian/intltool/fix-dangling-lock-file/+merge/400825)).

You may have the following error:
```
ERROR: files left in build directory after distclean:
./po/.intltool-merge-cache.lock
```

You need to fix it in Makefile.am as explained in https://gitlab.xfce.org/xfce/libxfce4ui/-/merge_requests/69 (https://gitlab.xfce.org/xfce/libxfce4ui/-/merge_requests/69) (Add `po/.intltool-merge-cache.lock` to DISTCLEANFILES target.)
Note: We will get rid of the deprecated intltool usage at a point with https://gitlab.xfce.org/xfce/xfce4-dev-tools/-/issues/41 (https://gitlab.xfce.org/xfce/xfce4-dev-tools/-/issues/41)

Enjoy :)
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