ci: Setup ramdisk for temp dir redirection

This step is no longer "hidden away in the infrastructure" but now in
the open.

Background: some GLib tests can fail with timeouts because of some
assumptions regarding the temporary directory that don't work out on
macOS. Until this is properly investigated and resolved, the
workaround is to redirect it to a ramdisk.

Also add ORKA_RUNNER variable as the macOS CI infrastructure evolves.
Future changes to the image can be controlled this way.

Fixes https://gitlab.gnome.org/Infrastructure/Infrastructure/-/issues/2091

.gitlab-ci.yml

@@ -795,9 +795,6 @@ freebsd-13-x86_64:
       - "_build/meson-logs"
 
 macos-arm64:
-  # FIXME: Temporarily disabled as the worker has issues creating temporary files
-  # See https://gitlab.gnome.org/Infrastructure/Infrastructure/-/issues/2091
-  when: manual
   extends: .only-default
   stage: build
   tags:
@@ -819,11 +816,13 @@ macos-arm64:
     SDKROOT: /opt/sdks/MacOSX11.3.sdk
     CCACHE_DIR: $CI_PROJECT_DIR/ccache
     CCACHE_MAXSIZE: "200Mi"
+    ORKA_RUNNER: sonoma-2
     # Redirect to the runner's volatile temporary directory which
     # unbreaks a couple of tests.
     TMPDIR: /Volumes/RAM
   before_script:
     - bash .gitlab-ci/show-execution-environment.sh
+    - diskutil erasevolume HFS+ "RAM" $(diskutil image attach ram://1GiB)
     - python3 -m venv .venv
     - ln -s /opt/ccache/ccache .venv/bin
     - source .venv/bin/activate