feat: officially support ruby <= 3.2

[sk-]

Description

Add Ruby 3.1 and 3.2 to the test matrix.

The performance benchmark was changed to use File.exist? as File.exists? was deprecated since Ruby 2.1 and finally removed in Ruby 3.2. See

Testing

This only changes the CI config and one benchmark.

References

• https://www.ruby-lang.org/en/news/2022/12/25/ruby-3-2-0-released/
• https://bugs.ruby-lang.org/issues/17391

[sk-]

Closing as there are other PRs doing the same.