Fix typo in triangular ldiv! (#43962)

(cherry picked from commit c3235cd)

Author: dkarrasch

stdlib/LinearAlgebra/src/triangular.jl

@@ -1486,7 +1486,7 @@ end
 function ldiv!(xA::Union{UpperTriangular,UnitUpperTriangular}, B::UpperTriangular)
     return UpperTriangular(ldiv!(xA, triu!(B.data)))
 end
-function ldiv!(xA::Union{LowerTriangular,UnitLowerTriangular}, B::UpperTriangular)
+function ldiv!(xA::Union{LowerTriangular,UnitLowerTriangular}, B::LowerTriangular)
     return LowerTriangular(ldiv!(xA, tril!(B.data)))
 end
 

stdlib/LinearAlgebra/test/triangular.jl

@@ -376,7 +376,8 @@ for elty1 in (Float32, Float64, BigFloat, ComplexF32, ComplexF64, Complex{BigFlo
                 @test_throws DimensionMismatch A2'  * offsizeA
                 @test_throws DimensionMismatch A2   * offsizeA
                 if (uplo1 == uplo2 && elty1 == elty2 != Int && t1 != UnitLowerTriangular && t1 != UnitUpperTriangular)
-                    @test rdiv!(copy(A1), copy(A2)) ≈ A1/A2 ≈ Matrix(A1)/Matrix(A2)
+                    @test rdiv!(copy(A1), copy(A2))::t1 ≈ A1/A2 ≈ Matrix(A1)/Matrix(A2)
+                    @test ldiv!(copy(A2), copy(A1))::t1 ≈ A2\A1 ≈ Matrix(A2)\Matrix(A1)
                 end
                 if (uplo1 != uplo2 && elty1 == elty2 != Int && t2 != UnitLowerTriangular && t2 != UnitUpperTriangular)
                     @test lmul!(adjoint(copy(A1)), copy(A2)) ≈ A1'*A2 ≈ Matrix(A1)'*Matrix(A2)