cicd: run on PRs

.github/workflows/docker-build.yml

@@ -1,12 +1,7 @@
 name: Build Docker image
 
 on:
-  push:
-    branches:
-      - 'master'
-      - 'staging'
-    tags:
-      - '*.*.*'
+  pull_request:
 
 jobs:
   docker:
@@ -20,7 +15,6 @@ jobs:
         id: meta
         uses: docker/metadata-action@v5
         with:
-          # list of Docker images to use as base name for tags
           images: pokeapi/pokeapi
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3