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

dev/bots/deploy_gallery.sh

diff --git a/dev/bots/deploy_gallery.sh b/dev/bots/deploy_gallery.sh
index 8e36ee6..06a82bd 100755
--- a/dev/bots/deploy_gallery.sh
+++ b/dev/bots/deploy_gallery.sh
@@ -44,7 +44,7 @@
     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

diff --git a/dev/ci/docker_linux/Dockerfile b/dev/ci/docker_linux/Dockerfile
index a42bd79..5b5d858 100644
--- a/dev/ci/docker_linux/Dockerfile
+++ b/dev/ci/docker_linux/Dockerfile
@@ -35,6 +35,7 @@
 RUN apt-get install -y --no-install-recommends \
   locales \
   ruby \
+  ruby-dev \
   nodejs \
   lib32stdc++6 \
   libstdc++6 \