Quotes in PR titles cause slack notification to fail

[zwolf]

PR titles are passed to the slack notification shared workflow via argument. When the PR contains double quotes (as here) they are not escaped properly and the action fails like this:

Run 8398a7/action-slack@v3
  with:
    job_name: Build Staging Image
    fields: took
    status: custom
    ...
  env:
    PR_URL: https://github.com/zooniverse/front-end-monorepo/pull/4436
    PR_TITLE: Classifier: change Annotate Button icon to "edit/pencil"
    SLACK_WEBHOOK_URL: ***
Error: Unexpected identifier 'edit'