Compare the Cirrus OS env var with the right value for macOS (darwin) (#22533)

dev/bots/deploy_gallery.sh

@@ -44,7 +44,7 @@ if [[ "$SHARD" = "deploy_gallery" ]]; then
     else
       echo "Not deployed: Flutter Gallery is only deployed to the Play Store on merged and tagged dev branch commits"
     fi
-  elif [[ "$OS" == "macos" ]]; then
+  elif [[ "$OS" == "darwin" ]]; then
     echo "Building Flutter Gallery $version for iOS..."
     (
       cd examples/flutter_gallery

dev/ci/docker_linux/Dockerfile

@@ -35,6 +35,7 @@ RUN bash "${NODEJS_INSTALL}/nodejs_install.sh"
 RUN apt-get install -y --no-install-recommends \
   locales \
   ruby \
+  ruby-dev \
   nodejs \
   lib32stdc++6 \
   libstdc++6 \