Deprecate and remove actions/install-requirement #250
Description
What is the problem or limitation you are having?
We currently publish the actions/install-requirement workflow, backed by the scripts/install_requirement.py script. This tool exists because we wanted to specify versions for tools like tox and pre-commit in GitHub actions workflows, and have them be automatically updated by dependabot - but without doing a pip install .[dev] install, because that requires installing the library itself.
However, this requirement has been essentially replaced by the use of dependency groups. Using dependency groups, it is possible to provide a specification for a tool in a way that dependabot can update, a GitHub action can reference without providing a version number, and can be installed without installing the base tool.
Describe the solution you'd like
Remove the use of the actions/install-requirement workflow in all remaining repositories, and then remove the workflow and script from this repository.
The only remaining uses at this point are:
- rubicon-objc (although that will be removed when Move to MkDocs from Sphinx. rubicon-objc#658 lands)
- Toga-chart (Switch to using dependency groups for dev/docs/test dependencies toga-chart#289 tracks removal)
- Colosseum (Switch to using dependency groups for dev/docs/test dependencies colosseum#177 tracks removal)
There were uses in Toga and Briefcase; those were removed as part of migrating to Mkdocs.
Describe alternatives you've considered
Additional context
This was noticed when beeware/briefcase#2502 landed - when that PR landed, the CI workflows verifying the install-requirements workflow failed, because the dev group no longer existed. The response in that case was to migrate to using toga-chart as a source of packages; but that workaround won't last long.