chore(build): use gha cache for PRs

Author: grampelberg

.github/workflows/docker.yml

@@ -70,8 +70,10 @@ jobs:
           file: docker/kty.dockerfile
           platforms: ${{ inputs.os }}/${{ inputs.arch }}
 
-          cache-from: type=registry,ref=${{ env.CACHE }}
-          cache-to: type=registry,ref=${{ env.CACHE }},mode=max
+          cache-from: |
+            ${{ inputs.arch == "arm64" && "type=registry,ref=${{ env.CACHE }}" || "type=gha" }}
+          cache-to: |
+            ${{ inputs.arch == "arm64" && "type=registry,ref=${{ env.CACHE }},mode=max" || "type=gha" }}
 
           labels: ${{ steps.meta.outputs.labels }}
           annotations: ${{ steps.meta.outputs.annotations }}