Update CompatHelper with permission to write PR (#172)

Author: adrhill

.github/workflows/CompatHelper.yml

@@ -8,6 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: write
+      pull-requests: write
     steps:
       - name: Pkg.add("CompatHelper")
         run: julia -e 'using Pkg; Pkg.add("CompatHelper")'