ci: Update validate-conventional-commits.yml (#23455)

Currently we are validating the PR title of PRs made against release
branches and master, but this breaks our release branching and PR
processes. For release candidate PRs, we don't want a conventional
commit title. This PR updates the conventional commit validation
workflow. As a result of this PR, we now follow the same approach as
mobile
https://github.com/MetaMask/metamask-mobile/blob/ef5febdc0964884352486b91b2cfe0e11f3fda29/.github/workflows/pr-title-linter.yml

.github/workflows/validate-conventional-commits.yml

@@ -1,6 +1,8 @@
 name: Validate Conventional Commit Title
 on:
   pull_request:
+    branches:
+      - develop
     types: [opened, edited, reopened]
 
 jobs: