Escape + in the branch name for the workflow trigger (#117)

According to
https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onpull_requestpull_request_targetbranchesbranches-ignore,
`+` that appears in the branch name needs to be escaped.

Co-authored-by: Eduardo Souza <[email protected]>

Author: qinsoon

.github/workflows/ci.yml

@@ -4,8 +4,8 @@ on:
   pull_request:
     branches:
       - master
-      - v1.8.2+RAI
-      - v1.9.2+RAI
+      - v1.8.2\+RAI
+      - v1.9.2\+RAI
 
 concurrency:
   # Cancels pending runs when a PR gets updated.