Update preferred Ruby version to 3.3, update deps (#1460)

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.

.github/workflows/publish-gem.yml

@@ -10,10 +10,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Setup Ruby 3.2
+    - name: Setup Ruby 3.3
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: "3.2"
+        ruby-version: "3.3"
 
     - name: Publish to GPR
       run: |