Migrate ubuntu-18.04 to ubuntu-latest using https://github.com/NerdWalletOSS/shepherd.
Test on macOS.
find .github/workflows -type f -name "*.y*ml" -exec grep "ubuntu-18.04" {} +;
find .github/workflows -type f -name "*.y*ml" -exec sed -i "" -e "s/ubuntu-18.04/ubuntu-latest/" {} +;