Updated CI workflow to run on PR label/unlabel

- We have browser tests which only run if the browser tests flag is added to the PR
- The label has to be present on PR creation, which is hard to remember/doesn't fit with various workflows
- The default type of action for the pull_request trigger are opened, synchronize, reopened
- This PR adds labeled and unlabeled to those, which I think will help us to run the tests as expected
- The expectation is that adding the browser test label will now trigger the tests to run

.github/workflows/ci.yml

@@ -1,6 +1,7 @@
 name: CI
 on:
   pull_request:
+    types: [opened, synchronize, reopened, labeled, unlabeled]
   push:
     branches:
       - main