Support using the required versions of needed/suggested packages

[wilfwilson]

This is the same request as gap-system/pkg-ci-scripts#3.

This would probably need to be a new separate action: you set up GAP with this action (probably with minimal packages), and then you would run a second action which would do the following.

• Get the needed/suggested other packages, and their versions, from the current package's PackageInfo.g file.
• Install (removing any existing versions as necessary) each of these packages in the correct version - possibly with PackageManager.

This would make it easy (I hope) to add a CI job that tests a package when used with the required versions of all its packages, and possibly in the required version of GAP, too. The intention would be to make it easy to work out when you should update the versions of your dependencies.

We currently have such tests for the Semigroups package (and we used to have them for Digraphs) and we find them useful.