Trying to fix rvm brew update error

tools/internal_ci/helper_scripts/prepare_build_macos_rc

@@ -36,11 +36,17 @@ fi
 
 if [ "${PREPARE_BUILD_INSTALL_DEPS_RUBY}" == "true" ]
 then
-  set +ex  # rvm script is very verbose and exits with errorcode
-  # Advice from https://github.com/Homebrew/homebrew-cask/issues/8629#issuecomment-68641176
-  brew update && brew upgrade brew-cask && brew cleanup && brew cask cleanup
-  set -e  # rvm commands are very verbose
+  brew update
+  # special case for https://github.com/grpc/grpc/issues/23027
+  rm -f /usr/local/bin/gpg
+  rm -f /usr/local/bin/gpgconf
+  rm -f /usr/local/bin/gpgsm
+  brew upgrade gnupg
+  # end https://github.com/grpc/grpc/issues/23027
+  brew cleanup
+  set +ex
   source $HOME/.rvm/scripts/rvm
+  set -ex
   for RUBY_VERSION in 2.5.0 2.7.0; do
     rvm --debug requirements "ruby-${RUBY_VERSION}"
     time rvm install "$RUBY_VERSION"
@@ -51,7 +57,6 @@ then
   time gem install cocoapods --version 1.3.1 --no-document
   rvm osx-ssl-certs status all
   rvm osx-ssl-certs update all
-  set -ex
 fi
 
 if [ "${PREPARE_BUILD_INSTALL_DEPS_OBJC}" == "true" ]