tests: add groups and project name to coverage

Groups make it easier to get an overview of the coverage without having
to scan through a single very long list of files. They also display a
possibly helpful per-group coverage.

The project name is normally derived from the `root` directory which
happens to be `Library` in our case, thus make it explicitly `Homebrew`.

Closes Homebrew/homebrew#49303.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>