This reduces dynamic dispatch and makes JET happier.
Testing on v1.11:
```julia
julia> import LinearAlgebra: checksquare

julia> using JET

julia> @report_opt checksquare(rand(2,2), rand(2,2))
═════ 4 possible errors found ═════
┌ checksquare(::Matrix{Float64}, ::Matrix{Float64}) @ LinearAlgebra /cache/build/builder-amdci4-1/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/LinearAlgebra/src/LinearAlgebra.jl:307
│┌ string(::String, ::Tuple{Int64, Int64}) @ Base ./strings/io.jl:189
││┌ print_to_string(::String, ::Tuple{Int64, Int64}) @ Base ./strings/io.jl:150
│││┌ _unsafe_take!(io::IOBuffer) @ Base ./iobuffer.jl:494
││││┌ wrap(::Type{Array}, m::MemoryRef{UInt8}, l::Int64) @ Base ./array.jl:3101
│││││ failed to optimize due to recursion: wrap(::Type{Array}, ::MemoryRef{UInt8}, ::Int64)
││││└────────────────────
│││┌ print_to_string(::String, ::Vararg{Any}) @ Base ./strings/io.jl:143
││││ runtime dispatch detected: Base._str_sizehint(%17::Any)::Int64
│││└────────────────────
│││┌ print_to_string(::String, ::Vararg{Any}) @ Base ./strings/io.jl:148
││││ runtime dispatch detected: print(%59::IOBuffer, %97::Any)::Any
│││└────────────────────
│││┌ string(::String, ::Int64, ::String, ::Tuple{Int64}, ::String, ::Int64, ::String, ::Int64, ::String) @ Base ./strings/io.jl:189
││││ failed to optimize due to recursion: string(::String, ::Int64, ::String, ::Tuple{Int64}, ::String, ::Int64, ::String, ::Int64, ::String)
│││└────────────────────

julia> function checksquare(A...) # This PR
                  sizes = Int[]
                  for a in A
                      size(a,1)==size(a,2) || throw(DimensionMismatch(lazy"matrix is not square: dimensions are $(size(a))"))
                      push!(sizes, size(a,1))
                  end
                  return sizes
              end
checksquare (generic function with 2 methods)

julia> @report_opt checksquare(rand(2,2), rand(2,2))
No errors detected

```