[skip-changelog] Pin `buf` to v1.4.0 (#1743)

The latest 1.5.0 requires go1.18+.

We could put it back to "latest" once we migrate to go1.18.

.github/workflows/check-protobuf-task.yml

@@ -95,9 +95,9 @@ jobs:
 
       - name: Install buf (protoc linter)
         run: |
-          go install github.com/bufbuild/buf/cmd/buf@latest
-          go install github.com/bufbuild/buf/cmd/protoc-gen-buf-breaking@latest
-          go install github.com/bufbuild/buf/cmd/protoc-gen-buf-lint@latest
+          go install github.com/bufbuild/buf/cmd/buf@v1.4.0
+          go install github.com/bufbuild/buf/cmd/protoc-gen-buf-breaking@v1.4.0
+          go install github.com/bufbuild/buf/cmd/protoc-gen-buf-lint@v1.4.0
 
       - name: Install Task
         uses: arduino/setup-task@v1