Add write permission for PR

Try fix GitHub Action error: actions/first-interaction#10

Author: vanillajonathan

.github/workflows/ci.yaml

@@ -5,6 +5,8 @@ on: [push, pull_request]
 jobs:
   build:
     runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
     strategy:
       matrix:
         python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]