triangular_solve: fix meta function output argument dtype check. (#140286)

Tracking issue: #138399
Pull Request resolved: https://github.com/pytorch/pytorch/pull/140286
Approved by: https://github.com/ezyang
ghstack dependencies: #140186

test/test_ops.py

@@ -222,7 +222,6 @@ meta_consistency_out_dtype_mismatch_xfails = {
     xfail("take"),
     xfail("transpose_copy"),
     xfail("tril"),
-    xfail("triangular_solve"),
     xfail("triu"),
     xfail("trunc"),
     xfail("unfold_copy"),

torch/_meta_registrations.py

@@ -1495,7 +1495,7 @@ def linalg_solve_triangular_meta(
 
 
 @register_meta(aten.triangular_solve)
-@out_wrapper("X", "M")
+@out_wrapper("X", "M", exact_dtype=True)
 def triangular_solve_meta(
     self: Tensor,
     A: Tensor,