CI: CMake: Separate build and test steps

[anzz1]

Otherwise the tests may be ran and pass even if the build has errors and thus the step itself can pass with errors in build

edit: separate build and test steps for all platforms.

[anzz1]

For future considerations:

In GitHub actions, each row of the run: commands are executed separately, irregardless what the previous input returned. The step determines "success" from the error code returned by the very last run command. As && means "execute if last output equals no error", cmake --build . --config Release && ctest -C Release --output-on-failure makes sure that the tests are only ran if the build succeeds, and that both needs to succeed for the CI step to return "success".

[anzz1]

Separated build and test steps as separate tasks as pointed out by @Green-Sky . Obviously should've done that in the first place, idk how I didn't think of that.

Also standardised the step id names between the platforms for 'cleanliness' sake (and possibly future expansion / easier build log scraping / etc).

[Green-Sky]

looks good.