[RF] Silence RooWorkspace unit test.
[RF] Silence RooWorkspace unit test.

The unit test for RooWorkspace tests failures when importing models into the workspace.
Since RooFit will print `ERROR` messages, it looks like there is a problem in the test.
The error messages are now silenced.
root-mirror/root,root-mirror/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,karies/root,karies/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,karies/root,olifre/root,karies/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root