ci: Avoid concurrency in PR CI (#836)

Author: mtrezza

.github/workflows/ci.yml

@@ -137,3 +137,6 @@ jobs:
         with:
           files: packages/dart/coverage/lcov.info
           fail_ci_if_error: true
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true