workflows/tests: run `brew typecheck --quiet`.

This will allow us to verify that we can merge new sorbet/tapioca
updates.

.github/workflows/tests.yml

@@ -120,6 +120,9 @@ jobs:
     - name: Run brew audit --skip-style on all taps
       run: brew audit --skip-style
 
+    # TODO: remove --quiet when possible.
+    - run: brew typecheck --quiet
+
     - name: Run vale for docs linting
       run: |
         brew install vale