fix: add explicit permissions to GitHub Actions workflows (#1246)

InfoSec is changing GITHUB_TOKEN default permissions from read/write
to read-only on July 15th. Adding explicit permissions blocks to all
workflows that require write access.

Author: flobernd

.github/workflows/backport.yml

@@ -5,6 +5,10 @@ on:
       - closed
       - labeled
 
+permissions:
+  contents: write
+  pull-requests: write
+
 jobs:
   backport:
     runs-on: ubuntu-latest