fix(ci): Fix RUNTIME_IMAGE_NAME variable substitution in runtime-base job

- Added RUNTIME_IMAGE_NAME to env section of Build and push runtime base image step
- Added RUNTIME_IMAGE_NAME to env section of Set runtime base outputs step
- Fixes 'bad substitution' error when variable is used in shell scripts

.gitea/workflows/build-image.yml

@@ -353,6 +353,7 @@ jobs:
         env:
           REGISTRY_URL: ${{ env.REGISTRY_URL }}
           CACHE_REGISTRY: ${{ env.CACHE_REGISTRY }}
+          RUNTIME_IMAGE_NAME: ${{ env.RUNTIME_IMAGE_NAME }}
         run: |
           cd /workspace/repo
 
@@ -363,7 +364,7 @@ jobs:
 
           echo "TARGET_REGISTRY=$TARGET_REGISTRY" >> $GITHUB_ENV
 
-          IMAGE_NAME="${{ env.RUNTIME_IMAGE_NAME }}"
+          IMAGE_NAME="$RUNTIME_IMAGE_NAME"
 
           echo "🏗️ Building runtime base image..."
           echo "   Registry: $TARGET_REGISTRY"
@@ -383,6 +384,8 @@ jobs:
       - name: Set runtime base outputs
         id: set-result
         shell: bash
+        env:
+          RUNTIME_IMAGE_NAME: ${{ env.RUNTIME_IMAGE_NAME }}
         run: |
           if [ "${{ steps.decision.outputs.should_build }}" = "true" ]; then
             TARGET_REGISTRY="${{ env.TARGET_REGISTRY || env.REGISTRY }}"