Downgraded documented ruby version to 3.1.0 (GoogleCloudPlatform#7370)

This should be a backwards-compatible change - users should be able to compile with either 3.2.0 or 3.1.0.

.ci/containers/downstream-builder/Dockerfile

@@ -17,7 +17,7 @@ RUN apt-get install -y bzip2 libssl-dev libreadline-dev zlib1g-dev unzip sed rsy
 RUN git clone https://github.com/rbenv/rbenv.git /rbenv
 ENV PATH /rbenv/bin:/root/.rbenv/shims:$PATH
 
-ENV RUBY_VERSION 3.2.0
+ENV RUBY_VERSION 3.1.0
 ENV RUBYGEMS_VERSION 3.4.1
 ENV BUNDLER_VERSION 2.4.6
 

.ruby-version

@@ -1 +1 @@
-3.2.0
+3.1.0

docs/content/docs/getting-started/setup.md

@@ -64,12 +64,12 @@ To get started, you'll need:
     instructions to set up Go: [YouTube video](https://www.youtube.com/watch?v=VQVyvulNnzs).
   * If you're using Cloud Shell, Go is already installed.
   * Currently it's recommended to use Go 1.18, Go 1.19 changed the gofmt rules which causes some gofmt issue and our CIs are all on 1.18.X
-* Ruby 3.2.0
+* Ruby 3.1.0
   * You can use [`rbenv`](https://github.com/rbenv/rbenv) to manage your Ruby version(s).
   * To install `rbenv`:
     * Homebrew: run `brew install rbenv ruby-build`
     * Debian, Ubuntu, and their derivatives: run `sudo apt install rbenv`
-  * Then run `rbenv install 3.2.0`.
+  * Then run `rbenv install 3.1.0`.
 * [`Bundler`](https://github.com/bundler/bundler)
   * This can be installed with `gem install bundler`
 * Gems for magic-modules
@@ -93,7 +93,7 @@ make doctor
 Check for rbenv in path...
    found!
 Checking ruby version...
-3.2.0 (set by [PATH]/magic-modules/mmv1/.ruby-version)
+3.1.0 (set by [PATH]/magic-modules/mmv1/.ruby-version)
 Check for bundler in path...
    found!
 Check for go in path...

mmv1/.ruby-version

@@ -1 +1 @@
-3.2.0
+3.1.0