`add generic syrk/herk` worsened effects of `*(::Matrix, ::Matrix)`

[adienes]

on cab0dc6 :

julia> Base.infer_effects(*, Tuple{Matrix{Int}, Matrix{Int}})
(!c,?e,!n,!t,+s,?m,!u,+o,+r)

but on a32a281 :

julia> Base.infer_effects(*, Tuple{Matrix{Int}, Matrix{Int}})
(!c,!e,!n,!t,!s,!m,!u,+o,!r)

this might be known / intentional, in which case please close this issue. but I am just assuming from the title of #1249 that it did not intend to have an impact on * methods of scalar matrices

[araujoms]

That was definitely not intentional. I don't know anything about these effects, so debugging will be challenging. Note that it wasn't for all scalars, though, I don't get any difference for BlasFloat.