ci: don't trigger on documentation-only commits

.github/workflows/build.yml

@@ -1,6 +1,13 @@
 name: 'Build (All)'
-
-on: [push, pull_request]
+on:
+  push:
+    paths-ignore:
+      - 'docs/**'
+      - '*.md'
+  pull_request:
+    paths-ignore:
+      - 'docs/**'
+      - '*.md'
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}