JRuby version 9.4.9.0

[schneems]

Changelog:

## JRuby version 9.4.9.0 is now available

[JRuby v9.4.9.0](/articles/ruby-support#ruby-versions) is now available on Heroku. To run 
your app using this version of Ruby, add the following `ruby` directive to your Gemfile:

```ruby
ruby "3.1.4", engine: "jruby", engine_version: "9.4.9.0"
```

The JRuby release notes can be found on the [JRuby website](https://www.jruby.org/news).

[colincasey]

@schneems your PR description had the main markdown content surrounded by a code fence containing an inner ruby code fence and this was causing the entry to be rendered incorrectly. I modified it to use indentation instead of a code fence for the outer one to avoid having to escape the inner code fence. Please check if this matches how you wanted this PR description to look.