Update GitHub Actions trigger and names in docker-build workflow

Converted the GitHub Actions trigger from 'on push' to 'on pull request' in the docker-build workflow file. This ensures a Docker image is built whenever a pull request is opened, edited or marked ready for review, allowing for more thorough CI checks. Also, added explicit names to checkout and setup steps for better readability and understanding of the workflow process.

.github/workflows/docker-bulid.yml

@@ -1,11 +1,14 @@
 name: GitHub Actions Demo
 run-name: ${{ github.actor }} is testing out GitHub Actions 🚀
-on: push
+on:
+  pull_request:
+    types: [opened, edited, ready_for_review]
 jobs:
   docker:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@master
+      - name: Git checkout
+        uses: actions/checkout@master
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v2
       - name: Set up Docker Buildx