Update to ruby 3.1.6 and set passenger_preload_bundler on to avoid gem version conflicts

[codycooperross]

To negotiate the following error in our staging deployment:

Error: The application encountered the following error: You have already activated forwardable 1.3.2, but your Gemfile requires forwardable 1.3.3. Since forwardable is a default gem, you can either remove your dependency on it or try updating to a newer version of bundler that supports forwardable as a default gem. (Gem::LoadError)

. . . this PR:

• Updates to Ruby 3.1.6
• Installs Bundler 2.6.9 in the Dockerfile and GitHub workflows
• Updates Gemfile.lock using Bundler 2.6.9
• Installs RubyGems 3.6.0 in the Dockerfile and GitHub workflows

This configuration is functional when the Docker container is running locally. Local requests used to trigger the Passenger error above.