ci: Add TTN PR number to merge-os-to-enterprise event

Author: vlasebian

.github/workflows/trigger-os-merge.yml

@@ -21,7 +21,8 @@ jobs:
             const resp = await github.rest.repos.createDispatchEvent({
               owner: 'TheThingsIndustries',
               repo: 'lorawan-stack',
-              event_type: 'merge-os-to-enterprise'
+              event_type: 'merge-os-to-enterprise',
+              ttn_pr_number: ${{ github.event.pull_request.number }}
             });
             if (resp.status !== 204) {
               throw new Error(`Failed to trigger OS merge action: ${resp.status} ${resp.statusText}`);