Re-enable "buf breaking" check (#4)

This restores the check, which was temporarily disabled
to push a change that the check didn't like (see #3).

.github/workflows/buf.yaml

@@ -8,21 +8,21 @@ jobs:
       - uses: actions/checkout@v3
       - uses: bufbuild/buf-setup-action@v1
       - uses: bufbuild/buf-lint-action@v1.0.3
-#  breaking:
-#    runs-on: ubuntu-20.04
-#    steps:
-#      - uses: actions/checkout@v3
-#      - uses: bufbuild/buf-setup-action@v1
-#      - uses: bufbuild/buf-breaking-action@v1.1.2
-#        with:
-#          against: buf.build/bufbuild/knit
+  breaking:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v3
+      - uses: bufbuild/buf-setup-action@v1
+      - uses: bufbuild/buf-breaking-action@v1.1.2
+        with:
+          against: buf.build/bufbuild/knit
   push:
     environment: production
     runs-on: ubuntu-20.04
     if: github.ref == 'refs/heads/main'
     needs:
       - lint
-#      - breaking
+      - breaking
     steps:
       - uses: actions/checkout@v3
       - uses: bufbuild/buf-setup-action@v1