Update GitHub Actions workflow for GPU build

.github/workflows/build_GPU.yml

@@ -3,8 +3,8 @@ name: Build_Subgen_Dockerfile_GPU
 on:
   push:
     paths:
-      - requirements.txt
-      - Dockerfile
+      - 'requirements.txt'
+      - 'Dockerfile'
   workflow_dispatch:
 
 jobs:
@@ -13,7 +13,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v2
         with:
           fetch-depth: 0
 
@@ -21,7 +21,7 @@ jobs:
         id: get_version
         run: |
           version=$(grep -oP "subgen_version\s*=\s*'\K[^']+" subgen.py)
-          echo "version=$version" >> "$GITHUB_ENV"
+          echo "version=$version" >> $GITHUB_ENV
 
       - name: Login to Docker Hub
         uses: docker/login-action@v3