Add filter-changes step

Author: bjw-s

.github/workflows/pre-pull-images.yaml

@@ -6,9 +6,6 @@ on:
   pull_request:
     branches:
       - main
-    paths:
-      - kubernetes/apps/**
-      - kubernetes/flux/**
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.number || github.ref }}
@@ -18,9 +15,27 @@ env:
   HOMEBREW_NO_ANALYTICS: "1"
 
 jobs:
+  filter-changes:
+    name: Filter changes
+    runs-on: ubuntu-latest
+    outputs:
+      any_changed: ${{ steps.changed-files.outputs.any_changed }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Get Changed Files
+        id: changed-files
+        uses: tj-actions/changed-files@v45
+        with:
+          files: kubernetes/**
+
   extract-images:
+    if: ${{ needs.filter-changes.outputs.any_changed == 'true' }}
     name: Extract Images
     runs-on: ubuntu-latest
+    needs:
+      - filter-changes
     strategy:
       matrix:
         branches: