ci: grant write permissions to GitHub Actions

semantic-release needs to be able to create git tags, so promote
the `contents` permission from `read` to `write` as indicated in
semantic-release/semantic-release#2496 (comment)

Author: ericcrosson-bitgo

.github/workflows/main_ci.yml

@@ -8,7 +8,7 @@ on:
   pull_request:
 
 permissions:
-  contents: read
+  contents: write
 
 jobs:
   ##################