This PR essentially updates the "default" Ruby version to 3.3. In the process, it:
- fixes a bug with the linux platform for `sass-embedded`
- regenerates the `Gemfile.lock` with Bundler 2.5.9
- adds Ruby 3.3 to the testing matrix & updates our deployment actions to use Ruby 3.3
- removes Ruby 3.0 from the testing matrix, as it is now end of life
This PR is motivated by https://github.com/just-the-docs/just-the-docs-template/pull/45, where I discovered that depending on the bundler/RubyGems version, the platform resolution for platformed gems can fail.
Ruby 3.2 has stabilized (and the bug with Liquid has been patched). I think this is a good time for us to bump all of our versions, especially with the discussion in #1307.
Separately, I've:
- changed the core test matrix to be across `3.0`, `3.1`, and `3.2`. Ruby 2 has been EOL for ~ 4 months, while 3.0 is around for about 7 more months.
- standardized the formatting of our CI ruby versions to be strings; this is because the number `3.0` gets YAML-casted to `3`
