Add support for Ruby 3.1 and Rails 7.0

This issue is a (choose one):

• Problem/bug report.
• Feature request.
• Request for support. Note: Please try to avoid submitting issues for support requests. Use Gitter instead.

Checklist before submitting:

• I've searched for an existing issue.
• I've asked my question on Gitter and have not received a satisfactory answer.
• I've included a complete bug report template. This step helps us and allows us to see the bug without trying to reproduce the problem from your description. It helps you because you will frequently detect if it's a problem specific to your project.
• The feature I'm asking for is compliant with the JSON:API spec.

Description

Features:

jsonapi-resources should support Ruby 3.1 and Rails 7.0, as these are now the most recently released versions of Ruby and Rails respectively. To ensure that these versions are supported, they need to be included in the CI matrix.

Start by locating the CI matrix and its existing Ruby and Rails version entries. Update the matrix to include Ruby 3.1 and Rails 7.0, then run the CI checks to confirm the new combinations pass.