Remove rbs:confirm task from sig.yml workflow

Co-authored-by: hsbt <12301+hsbt@users.noreply.github.com>

Author: Copilot

.github/workflows/sig.yml

@@ -16,5 +16,5 @@ jobs:
         run: |
           bundle config set with 'sig'
           bundle install
-      - name: Run RBS test and confirm
-        run: bundle exec rake rbs:{test,confirm}
+      - name: Run RBS test
+        run: bundle exec rake rbs:test