fix: use PR mode for spec-change SDK generation

Switch sdk_generation_for_spec_change.yaml from direct to pr mode so
Speakeasy opens a PR instead of pushing to main. This avoids branch
protection failures and routes publishing through sdk_publish.yaml.

.github/workflows/sdk_generation_for_spec_change.yaml

@@ -28,7 +28,7 @@ jobs:
     uses: speakeasy-api/sdk-generation-action/.github/workflows/workflow-executor.yaml@v15
     with:
       force: ${{ github.event.inputs.force }}
-      mode: direct
+      mode: pr
       set_version: ${{ github.event.inputs.set_version }}
     secrets:
       github_access_token: ${{ secrets.GITHUB_TOKEN }}