ci: Rename .ci-run-policy rules to .build-rules.

... and explain what they're doing, compared to the test rules in
test-source-dep.yml.

Unfortunately, we can't really pull them into test-source-dep.yml with
other source deps, because of various '&'-'*' references.

Acked-by: Michel Dänzer <mdaenzer@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17386>

.gitlab-ci/test-source-dep.yml

@@ -14,8 +14,8 @@
     - if: *is-scheduled-pipeline
       when: never
 
-# Mesa core source file dependencies that may impact any build or test.
-# ---------------------------------------------------------------------
+# Mesa core source file dependencies that may impact any test job
+# ---------------------------------------------------------------
 .core-rules:
   rules:
     - !reference [.no_scheduled_pipelines-rules, rules]
@@ -39,7 +39,7 @@
       - src/util/**/*
       when: on_success
 
-# Mesa source file dependencies that may impact any GL driver build or test.
+# Mesa source file dependencies that may impact any GL driver test job.
 .gl-rules:
   rules:
     - !reference [.core-rules, rules]