fix(release): drop arithmetic from dispatch job name (DataDog#23541)

GitHub Actions expressions don't support arithmetic operators, so
`strategy.job-index + 1` made the workflow file invalid. Use the
0-indexed `strategy.job-index` directly.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: dkirov-dd

.github/workflows/release-dispatch.yml

@@ -92,7 +92,7 @@ jobs:
         run: python .github/workflows/scripts/release_dispatch.py
 
   dispatch:
-    name: Dispatch wheel builds (batch ${{ strategy.job-index + 1 }})
+    name: Dispatch wheel builds (batch ${{ strategy.job-index }})
     needs: prepare
     if: needs.prepare.outputs.has_packages == 'true' && !inputs.dry-run
     runs-on: ubuntu-latest