CircleCI bump fails tests with Ruby update

[miketheman]

What Renovate type are you using?
Renovate GitHub App

Describe the bug
During a CircleCI version bump of the Ruby runtime in the tests, automated CI tests fail due to a Ruby version mismatch.

Did you see anything helpful in debug logs?
Job Log 43241196

To Reproduce
Steps to reproduce the behavior:

1. Create repository with a Gemfile with ruby '2.6.0' and a CircleCI .circleci/config.yml with - image: circleci/ruby:2.6.0-node-browsers in the docker section
2. Configure renovatebot for the repo (default, extends base)
3. A PR for 'Update circleci/ruby Docker tag to v2.6.1' should be generated, and a failing build should occur:

#!/bin/bash -eo pipefail
bundle check || bundle install
Your Ruby version is 2.6.1, but your Gemfile specified 2.6.0
Your Ruby version is 2.6.1, but your Gemfile specified 2.6.0

Expected behavior
A passing build - perhaps a bump in the Gemfile and Gemfile.lock as part of the same PR

Additional context
Uncertain of where the responsibility lies for a runtime upgrade, as this could be part of the user's responsibility to ensure that each component is in a working state before committing.
It's entirely possible this kind of update should be treated differently, which in that case, there's probably some other messaging to provide around runtime updates.

[rarkins]

For Node.js, we currently try to catch all possible locations it's defined and upgrade the in the same PR. I think for Ruby we can do the same, although it's still a work in progress. Gemfile support is still in alpha for example, and we need to add ruby 'x' upgrading to it. Another location is the .ruby-version file (#3090).

[rarkins]

Waiting on #3090

[aaronjensen]

And .tool-versions #4051

[HonkingGoose]

Issue #3090 is resolved now, but we're still waiting on:

• Upgrade versions in .tool-versions #4051