Add dependabot ignore for awalsh128/cache-apt-pkgs-action (#8495)

Author: cknitt

.github/dependabot.yml

@@ -10,4 +10,8 @@ updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "weekly"
+      interval: "weekly"
+    ignore:
+      # Versions >1.4.3 interfere with caching done by our own CI script,
+      # causing the dune binary not to be found anymore.
+      - dependency-name: "awalsh128/cache-apt-pkgs-action"