Fix GITHUB_TOKEN env var

Author: fr4nc1sc0-r4m0n

.github/workflows/merge-upstream-test.yaml

@@ -58,7 +58,7 @@ jobs:
         if: steps.check.outputs.commits_behind != '0'
         id: create_pr
         env:
-          GH_TOKEN: ${{ steps.get_token.outputs.token }}
+          GITHUB_TOKEN: ${{ steps.get_token.outputs.token }}
         run: |
           PR_URL=$(gh pr create \
             --title "chore: merge with upstream opentelemetry-demo" \