Workflow that tests without suggested dependencies

[krlmlr]

A matrix for each suggested and enhanced package, where we omit only the corresponding package in each run.

Example: suggests rlang, vctrs, igraph.

Three runs, in a matrix:

1. without rlang + vctrs
2. without vctrs
3. without igraph

https://www.cynkra.com/blog/2020-12-23-dynamic-gha/