chore: update preview ID message to clarify Mintlify (#1165)

Author: mdrxy

.github/workflows/create-preview-branch.yml

@@ -175,5 +175,5 @@ jobs:
               owner: context.repo.owner,
               repo: context.repo.repo,
               issue_number: context.issue.number,
-              body: `Preview ID generated: ${preview}`
+              body: `Mintlify preview ID generated: ${preview}`
             });