gitlab-ci: Only run the pipeline if any files affecting it have changed

E.g. documentation-only changes cannot affect the outcome of the
pipeline, so don't waste resources on running it.

The thing we need to be careful about here is that the container stage
jobs must always run if any later stage jobs using the corresponding
docker images run. We're currently using the same .ci-run-policy
template for all jobs, so this is trivially true.

v2:
* Add bin/ and common.py (Eric Engestrom)

Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com> # v1
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

.gitlab-ci.yml

@@ -40,9 +40,27 @@ stages:
 # When to automatically run the CI
 .ci-run-policy:
   only:
-    - branches@mesa/mesa
-    - merge_requests
-    - /^ci([-/].*)?$/
+    refs:
+      - branches@mesa/mesa
+      - merge_requests
+      - /^ci([-/].*)?$/
+    changes:
+      - VERSION
+      - bin/**/*
+      # GitLab CI
+      - .gitlab-ci.yml
+      - .gitlab-ci/**/*
+      # Meson
+      - meson*
+      - build-support/**/*
+      - subprojects/**/*
+      # SCons
+      - SConstruct
+      - scons/**/*
+      - common.py
+      # Source code
+      - include/**/*
+      - src/**/*
   retry:
     max: 2
     when: