CI: arch: fix failing to detect any glib ecosystem tools

Due to reasons, Arch has chosen to split out the glib2 package into a
glib2-devel package containing a small handful of python programs. The
references to these programs are contained in the main glib2 package, so
meson fails a lot in CI with e.g.

```
test cases/frameworks/7 gnome/gdbus/meson.build:1:18: ERROR: Dependency 'gio-2.0' tool variable 'gdbus_codegen' contains erroneous value: '/usr/bin/gdbus-codegen'

This is a distributor issue -- please report it to your gio-2.0 provider.
```

ci/ciimage/arch/install.sh

@@ -11,7 +11,7 @@ pkgs=(
   ninja make git sudo fakeroot autoconf automake patch
   libelf gcc gcc-fortran gcc-objc vala rust bison flex cython go dlang-dmd
   mono boost qt5-base gtkmm3 gtest gmock protobuf gobject-introspection
-  itstool gtk3 java-environment=8 gtk-doc llvm clang sdl2 graphviz
+  itstool glib2-devel gtk3 java-environment=8 gtk-doc llvm clang sdl2 graphviz
   doxygen vulkan-validation-layers openssh mercurial gtk-sharp-2 qt5-tools
   libwmf cmake netcdf-fortran openmpi nasm gnustep-base gettext
   python-lxml hotdoc rust-bindgen qt6-base qt6-tools wayland wayland-protocols