bootstrap: fix build_tools error
bootstrap: fix build_tools error

If `setuptools.version` contains a string, an error occurs.
So, it was modified to extract only semver from `version`.

Part-of: <https://gitlab.freedesktop.org/gstreamer/cerbero/-/merge_requests/711>

nirbheek/cerbero,nirbheek/cerbero,nirbheek/cerbero,nirbheek/cerbero