chore(actions): Backport action needs contents write. (#644)

Accidentally set the contents permission to read so now the backports
cannot be created.

Author: mcottontensor

.github/workflows/backport.yml

@@ -5,7 +5,7 @@ on:
     types: ["labeled", "closed"]
 
 permissions:
-  contents: read
+  contents: write
   pull-requests: write
 
 jobs: