using ref to checkout

.github/workflows/docker.yml

@@ -2,7 +2,12 @@ name: Publish Docker image
 
 on:
   workflow_dispatch:
-    inputs: null
+    inputs:
+      LABS:
+        description: 'Labs version'
+        required: true
+        default: 'v2.1'
+        type: string
 
 jobs:
 
@@ -12,6 +17,8 @@ jobs:
     steps:
       - name: Check out the repo
         uses: actions/checkout@v3
+        with:
+          ref: ${{ inputs.LABS }}
 	  
       - name: Log in to Docker Hub
         uses: docker/login-action@v2