build: Bump Meson dependency to 1.2.0

And update all the CI builds to use the latest micro release from that
series, 1.2.3.

This version bump means we can:
 - Drop some backwards-compatibility Meson checks
 - Fix a periodic CI failure caused by a now-fixed Meson bug
   (https://github.com/mesonbuild/meson/pull/10633)

It’s in line with our [Meson version policy](./docs/meson-version.md),
as Meson 1.2.1 is available in
[Debian Trixie](https://packages.debian.org/source/trixie/meson) and the
[freedesktop SDK](c95902f2ed/elements/components/meson.bst).

Signed-off-by: Philip Withnall <philip@tecnocode.co.uk>

.gitlab-ci/fedora.Dockerfile

@@ -75,7 +75,7 @@ RUN dnf -y update \
     make \
  && dnf clean all
 
-RUN pip3 install meson==0.60.3
+RUN pip3 install meson==1.2.3
 
 COPY install-gitlab-cobertura-tools.sh .
 RUN ./install-gitlab-cobertura-tools.sh