Fix traceback when running osc from an arbitrary git repo that fails …

…to map branch to a project (boo#1218170)

osc/git_scm/store.py

@@ -76,7 +76,7 @@ def project(self):
             if branch == "factory":
                 self._project = "openSUSE:Factory"
             else:
-                raise RuntimeError(f"Couldn't map git branch '{branch}' to a project")
+                raise oscerr.NoWorkingCopy(f"Couldn't map git branch '{branch}' to a project")
         return self._project
 
     @project.setter