Update trigger_nightly.yml to add torchtitan (#6924)

Add torchtitan to the nightly build trigger so that every night, `main`
is cut into a `nightly` branch, which can then be built and released on
the PyTorch Index.

Pre-reqs: @tianyu-l has already added the pytorch-bot to the torchtitan
repo and given it write permissions.

Author: joecummings

.github/workflows/trigger_nightly.yml

@@ -23,6 +23,7 @@ on:
           - torchtune
           - torchcodec
           - torchvision-extra-decoders
+          - torchtitan
           - all
 jobs:
   trigger:
@@ -119,3 +120,11 @@ jobs:
           repository: pytorch-labs/torchvision-extra-decoders
           token: ${{ secrets.GH_PYTORCHBOT_TOKEN }}
           path: torchvision-extra-decoders
+      - name: Trigger nightly torchtitan
+        if: ${{ github.event_name == 'schedule' ||  inputs.domain == 'torchtitan' || inputs.domain == 'all' }}
+        uses: ./.github/actions/trigger-nightly
+        with:
+          ref: main
+          repository: pytorch/torchtitan
+          token: ${{ secrets.GH_PYTORCHBOT_TOKEN }}
+          path: torchtitan