ci: Use correct sed command to bump version of jupyter images

The version of the image is not attached to it. Instead, if it specified
in the line right below, both for the system user and jupyterhub images

.github/workflows/update-images.yaml

@@ -21,10 +21,10 @@ jobs:
 
     - name: Update images version
       run: |
-        echo "Updating information for image = ${{ github.event.inputs.image }} version = ${{ github.event.inputs.version }}"
         export IMAGE_NAME=${{ github.event.inputs.image }}
-        export IMAGE_VERSION=$(echo ${{ github.event.inputs.version }} | sed -e "s/v//g")
-        sed -i "s|\(gitlab-registry.cern.ch/swan/docker-images/$IMAGE_NAME:\)[^ ]*|\1$IMAGE_VERSION|" swan/values.yaml
+        export IMAGE_VERSION=${{ github.event.inputs.version }}
+        echo "Updating information for image = $IMAGE_NAME version = $IMAGE_VERSION"
+        sed -i "\|gitlab-registry.cern.ch/swan/docker-images/$IMAGE_NAME|!b;n;s|tag: .*|tag: $IMAGE_VERSION|" swan/values.yaml
     - name: Create Pull Request
       id: cpr
       uses: peter-evans/create-pull-request@v6