Add patch to Ruby version in dev.yml

[sambostock]

Motivation

With the patch, Dev downloads a precompiled binary, but without it seems to choose to compile from source, which seems unnecessary.

Implementation

The config is updated to Ruby 3.1.2, the latest in the 3.1 releases.

Tests

🎩'd locally.

[sambostock]

CI failures seem unrelated. I was able to push an empty commit based on main and replicate the failures.

It consistently fails only on the following test, only on builds using Rails 6.1:

Tapioca
  Gem
    Pipeline
      it compiles constants of generic types                            ERROR (0.02s)
Minitest::UnexpectedError:
  TypeError: T.let: Expected type GenericInterface[::Numeric],
                         got type Concrete with hash 4102188866738066998
    Caller: /tmp/d20...1mo/lib/generic.rb:16
            /tmp/d20...1mo/lib/generic.rb:16:in `<top (required)>'
            .../tapioca/lib/tapioca.rb:23:in `block in silence_warnings'
            [...]
            .../tapioca/spec/tapioca/gem/pipeline_spec.rb:3328:in `block (2 levels) in <class:PipelineSpec>'

Update: Resolving this is being worked on in #1270

[Morriar]

With the patch, Dev downloads a precompiled binary, but without it seems to choose to compile from source, which seems unnecessary.

Should we add this as a comment explaining why we use this version?

[sambostock]

🤷‍♂️ I've never seen it in other projects. This tends to be "latest stable" anyway.

[sambostock]

Searching for x.y Ruby versions in dev.yml across our org only turns up 5 matches, so I think it's safe to say this is uncommon.