Refactor the CI configuration to use inclusion instead of exclusion

[Flamefire]

This provides more clarity on what exactly is run

The jobs have not changed, the following configurations are tested before (and after):

build (2.7, Lmod-7.8.22, Lua)
build (2.7, Lmod-7.8.22, Tcl)
build (2.7, Lmod-8.2.9, Lua)
build (2.7, Lmod-8.2.9, Tcl)
build (2.7, modules-tcl-1.147, Tcl)
build (2.7, modules-3.2.10, Tcl)
build (2.7, modules-4.1.4, Tcl)

build (3.6, Lmod-7.8.22, Lua)
build (3.6, Lmod-7.8.22, Tcl)
build (3.6, Lmod-8.2.9, Lua)
build (3.6, Lmod-8.2.9, Tcl)
build (3.6, modules-tcl-1.147, Tcl)
build (3.6, modules-3.2.10, Tcl)
build (3.6, modules-4.1.4, Tcl)

build (3.5, Lmod-8.2.9, Lua)
build (3.5, Lmod-8.2.9, Tcl)

build (3.7, Lmod-8.2.9, Lua)
build (3.7, Lmod-8.2.9, Tcl)

build (3.8, Lmod-8.2.9, Lua)
build (3.8, Lmod-8.2.9, Tcl)

build (3.9, Lmod-8.2.9, Lua)
build (3.9, Lmod-8.2.9, Tcl)

build (3.6, Lmod-8.2.9, Lua, C)

[boegel]

@Flamefire lgtm, that looks a bit cleaner indeed.
Let's bump to the latest Lmod 8.x while we're at it: Flamefire#7

[Flamefire]

I'd like to try something more: Avoid the repetition of the lmod version.
It seems you can generate a whole matrix from within a job step: https://docs.github.com/en/actions/reference/context-and-expression-syntax-for-github-actions#example-returning-a-json-object

But what we just need here is something we can access with ${{}}, e.g. an env variable.
I'll try that later, so hold up the merge please :)

Lmod version bumped

[boegel]

I'd like to try something more: Avoid the repetition of the lmod version.
It seems you can generate a whole matrix from within a job step: https://docs.github.com/en/actions/reference/context-and-expression-syntax-for-github-actions#example-returning-a-json-object

But what we just need here is something we can access with ${{}}, e.g. an env variable.
I'll try that later, so hold up the merge please :)

OK! :)

[boegel]

@Flamefire Once you're happy with the changes, I'll need to re-configure the test configurations that are required to pass (which is why there's a bunch of orange dots sitting there "waiting" right now).

[Flamefire]

I think this works now. What do you think about this approach?
Alternative:

env:
  LMOD_7: Lmod-...
  ...
  modules_tool: [${env.LMOD_7}, ...]

That's a bit shorter but sets those as actual env variables, so my current approach feels "more right"

[boegel]

lgtm