build: Use explicit date version number for dev container

This removes the requirement to ensure that we land PRs that update the
Dockerfile (and the appropraite dev_cli.sh change) in a specific time
frame.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>

.github/workflows/docker-image.yaml

@@ -41,7 +41,7 @@ jobs:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
           # generate Docker tags based on the following events/attributes
           tags: |
-            type=raw,value={{date 'YYYYMMDD'}}-0
+            type=raw,value=20240407-0
             type=sha
 
       - name: Build and push