Set the target deployment to main during dispatched documentation deployments (#7304)

Closes #7276 by deploying to production when not triggered by a pull
request.

Author: zanieb

.github/workflows/docs.yaml

@@ -51,4 +51,5 @@ jobs:
         with:
           apiToken: ${{ secrets.CF_API_TOKEN }}
           accountId: ${{ secrets.CF_ACCOUNT_ID }}
-          command: pages deploy site --project-name=ruff-docs --branch ${GITHUB_HEAD_REF} --commit-hash ${GITHUB_SHA}
+          # `github.head_ref` is only set during pull requests and for manual runs or tags we use `main` to deploy to production
+          command: pages deploy site --project-name=ruff-docs --branch ${{ github.head_ref || 'main' }} --commit-hash ${GITHUB_SHA}