Fix duplicate rules: key in meson-format CI job

The meson-format job had two `rules:` blocks. YAML silently overwrites
the first with the second, so the job only ran on MRs with meson.build
changes. The intended rules (tags, schedules, other pipeline sources)
were silently discarded. Remove the duplicate to restore the original
intent.

Assisted-by: Claude:claude-opus-4-7

.gitlab-ci.yml

@@ -766,10 +766,6 @@ meson-format:
       - meson-format.patch
     expire_in: "1 week"
     when: on_failure
-  rules:
-    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
-      changes:
-        - "**/meson.build"
 
 doctest:
   <<: *quick_checks_job