Check for Method return from jl_gf_invoke_lookup

Fixes timholy/Revise.jl#515
Changed in JuliaLang/julia#35983

Author: timholy

src/utils.jl

@@ -34,6 +34,7 @@ function whichtt(@nospecialize(tt))
     # TODO: provide explicit control over world age? In case we ever need to call "old" methods.
     m = ccall(:jl_gf_invoke_lookup, Any, (Any, UInt), tt, typemax(UInt))
     m === nothing && return nothing
+    isa(m, Method) && return m
     return m.func::Method
 end