ci: Make MALLOC_PERTURB_ less random

The point is to not initialize to some non-zero value to find places
incorrectly relying on blocks being zero initialized. Thus, there is no
reason to have a different random number each time, and by having it the
same, we have slightly more reproducable triggers, would we ever trigger
anything due to this.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/591

.gitlab-ci.yml

@@ -37,12 +37,12 @@ test-mutter:
     GSETTINGS_SCHEMA_DIR: "$CI_PROJECT_DIR/build/data"
     MALLOC_CHECK_: "3"
     NO_AT_BRIDGE: "1"
+    MALLOC_PERTURB_: "123"
   script:
     - dconf update
     - mkdir -m 700 $XDG_RUNTIME_DIR
     - glib-compile-schemas $GSETTINGS_SCHEMA_DIR
     - >
-      env MALLOC_PERTURB_="$((RANDOM % 256 + 1))"
       dbus-run-session -- xvfb-run -s '+iglx -noreset'
       meson test -C build --no-rebuild -t 10 --verbose --no-stdsplit --wrap catchsegv
   only: