Updated CI

Author: ankane

.github/workflows/build.yml

@@ -18,7 +18,7 @@ jobs:
       - run: bundle exec rake vendor:platform
       - run: bundle exec rake test
 
-      - if: ${{ matrix.valgrind }}
+      - if: ${{ startsWith(matrix.os, 'ubuntu') }}
         run: |
           sudo apt-get update && sudo apt-get install valgrind
           bundle exec rake test:valgrind