CI: Install meson from bookworm-backports when using GLib subproject

Debian 12 'bookworm' has Meson 1.0.1, which is too old for the current
stable branch of GLib. Use the version from bookworm-backports when
running on Debian and building with a mingw-w64 compiler.

We can stop doing this and put meson back in the normal list of
packages when we update to the Debian 13 stable release, expected to be
released in mid 2025.

Signed-off-by: Simon McVittie <smcv@collabora.com>

tools/ci-install.sh

@@ -91,9 +91,19 @@ case "$ci_distro" in
                 ;;
         esac
 
-        $sudo apt-get -qq -y update
         packages=()
 
+        case "$ci_host/$ci_suite" in
+            (*-w64-mingw32/bookworm)
+                echo "deb https://deb.debian.org/debian bookworm-backports main" >> /etc/apt/sources.list.d/backports.list
+                packages=("${packages[@]}" meson/bookworm-backports)
+                ;;
+
+            (*)
+                packages=("${packages[@]}" meson)
+                ;;
+        esac
+
         case "$ci_host" in
             (i686-w64-mingw32)
                 packages=(
@@ -148,7 +158,6 @@ case "$ci_distro" in
             libsystemd-dev
             libx11-dev
             llvm
-            meson
             ninja-build
             sudo
             valgrind
@@ -161,6 +170,7 @@ case "$ci_distro" in
             zstd
         )
 
+        $sudo apt-get -qq -y update
         $sudo apt-get -qq -y --no-install-recommends install "${packages[@]}"
 
         packages=(