bugfix: properly import Base.cis into LinearAlgebra (#42164)

Certain methods, e.g.,
`cis(::Union{RealHermSymComplexHerm,SymTridiagonal{<:Real}})`,
were not imported properly.

(cherry picked from commit c4f0d8b)

Author: olof3

stdlib/LinearAlgebra/src/LinearAlgebra.jl

@@ -9,7 +9,7 @@ module LinearAlgebra
 
 import Base: \, /, *, ^, +, -, ==
 import Base: USE_BLAS64, abs, acos, acosh, acot, acoth, acsc, acsch, adjoint, asec, asech,
-    asin, asinh, atan, atanh, axes, big, broadcast, ceil, conj, convert, copy, copyto!, cos,
+    asin, asinh, atan, atanh, axes, big, broadcast, ceil, cis, conj, convert, copy, copyto!, cos,
     cosh, cot, coth, csc, csch, eltype, exp, fill!, floor, getindex, hcat,
     getproperty, imag, inv, isapprox, isequal, isone, iszero, IndexStyle, kron, kron!, length, log, map, ndims,
     oneunit, parent, power_by_squaring, print_matrix, promote_rule, real, round, sec, sech,

stdlib/LinearAlgebra/src/dense.jl

@@ -576,8 +576,8 @@ julia> cis([π 0; 0 π]) ≈ -I
 true
 ```
 """
-Base.cis(A::AbstractMatrix) = exp(im * A)  # fallback
-Base.cis(A::AbstractMatrix{<:Base.HWNumber}) = exp_maybe_inplace(float.(im .* A))
+cis(A::AbstractMatrix) = exp(im * A)  # fallback
+cis(A::AbstractMatrix{<:Base.HWNumber}) = exp_maybe_inplace(float.(im .* A))
 
 exp_maybe_inplace(A::StridedMatrix{<:Union{ComplexF32, ComplexF64}}) = exp!(A)
 exp_maybe_inplace(A) = exp(A)