ci: add SKIP_COMMIT logic to update-demo script

Make it testable locally.

tasks/stages/update-demo

@@ -1,5 +1,6 @@
 #!/bin/bash
 
+
 # bumps bpmn-js and diagram-js dependencies in bpmn-io-demo
 
 PWD="$(pwd)"
@@ -15,14 +16,19 @@ cd "$CLONE_DIR"
 
 npm install --save bpmn-js@latest diagram-js@latest
 
+if [[ "x$SKIP_COMMIT" = "x" ]]; then
+
   git config user.email "$BPMN_IO_EMAIL"
   git config user.name "$BPMN_IO_USERNAME"
   git config push.default simple
 
   git add -A
-git commit -m "deps: bump bpmn-js to $TAG"
+  git commit -m "deps: bump to bpmn-js@$TAG"
   git tag "bpmn-js-$TAG"
   git push -q &2>/dev/null
   git push --tags -q &2>/dev/null
+else
+  echo "Skipping commit (SKIP_COMMIT=$SKIP_COMMIT)"
+fi
 
 cd "$PWD"