more CI tests

[umlaeute]

in the wake of #243 i decided that it is probably best to run the test-suite on the CI, so we can catch issues here early.

this PR attempts to implement this:

• it adds a new job Linux that builds libmysofa and runs the tests
• it splits the existing Windows job into:
  • a CommitInfo job that extracts the information for the release version
  • the Windows job that only builds libmysofa and generates some artifacts
  • a PreRelease job that creates a pre-release and attaches the Windows-artifacts to it.

in my fork of the project, the PreRelease step fails, but that was also the case in the original Windows job, so I don't think this is a regression (but couldn't actually test)