Prefer-lowest build uses installer version that may not be the lowest that module supports

[GuySartorelli]

Prefer-lowest builds install the version of installer that all the other CI runs use, which may not respect the actual dependencies for the module. This can result in problems we aren't catching when we forget to bump dependencies.

Acceptance criteria

• When CI runs include an installer version being added by the matrix, the version of installer used in the prefer-lowest build is the lowest version allowed in the dependencies for that module

PRs

• https://github.com/silverstripe/gha-generate-matrix/pull/97
• https://github.com/silverstripe/gha-ci/pull/130

[emteknetnz]

Example run https://github.com/emteknetnz/silverstripe-elemental/actions/runs/9752302859

Composer bit looks like this running on the 5 branch for the --prefer-lowest build:

All other jobs just use installer 5.x-dev