🐛 Update Direct solver to behave the same as Shell solver

- In the case of `noSolution`, CPLEXSHELL now considers this a `warning` solver status
- Similarly, `GAMSDirect` returns a `SolutionStatus.unknown` so we should be consistent with that

pyomo/solvers/plugins/solvers/cplex_direct.py

@@ -562,9 +562,9 @@ def _postsolve(self):
         } or self._error_code == self._cplex.exceptions.error_codes.CPXERR_NO_SOLN:
             # CPLEX doesn't have a solution status for `noSolution` so we assume this from the combination of
             # maxTimeLimit + infeasible (instead of a generic `TerminationCondition.error`).
-            self.results.solver.status = SolverStatus.error
+            self.results.solver.status = SolverStatus.warning
             self.results.solver.termination_condition = TerminationCondition.noSolution
-            soln.status = SolutionStatus.error
+            soln.status = SolutionStatus.unknown
         else:
             self.results.solver.status = SolverStatus.error
             self.results.solver.termination_condition = TerminationCondition.error