[Docs] fix typo in example of torch.linalg.solve_triangular (pytorc…

…h#112361)

Fixes pytorch#112359

Pull Request resolved: pytorch#112361
Approved by: https://github.com/IvanYashchuk

torch/linalg/__init__.py

@@ -2242,7 +2242,7 @@
 Examples::
 
     >>> A = torch.randn(3, 3).triu_()
-    >>> b = torch.randn(3, 4)
+    >>> B = torch.randn(3, 4)
     >>> X = torch.linalg.solve_triangular(A, B, upper=True)
     >>> torch.allclose(A @ X, B)
     True