Update install_test_workflow_prereqs.sh (#1081)

Author: sunmou99

scripts/gha/install_test_workflow_prereqs.sh

@@ -56,7 +56,6 @@ fi
 
 if [[ "${OS}" == "Mac" ]]; then
  sudo xcode-select -s /Applications/Xcode_${xcodeVersion}.app/Contents/Developer
- brew update
 fi
 
 if [[ "${PLATFORM}" == "Desktop" ]]; then