fix broadcast on Base.rewrap_unionall in alltypesigs

For me this fixes #102

Problematic use-case is roughly as follows:
```
julia> sig = (Tuple{G} where G)
Tuple{G} where G

julia> Base.rewrap_unionall.(DocStringExtensions.uniontypes(Base.unwrap_unionall(sig)), sig)
1-element Vector{DataType}:
 Tuple{G}

julia> Base.rewrap_unionall.(DocStringExtensions.uniontypes(Base.unwrap_unionall(sig)), Ref(sig))
1-element Vector{UnionAll}:
 Tuple{G} where G
```

Author: exaexa

src/utilities.jl

@@ -111,7 +111,8 @@ function alltypesigs(sig)::Vector{Any}
     elseif isa(sig, Union)
         uniontypes(sig)
     elseif isa(sig, UnionAll)
-        Base.rewrap_unionall.(uniontypes(Base.unwrap_unionall(sig)), sig)
+        Any[Base.rewrap_unionall(usig, sig) for
+            usig in uniontypes(Base.unwrap_unionall(sig))]
     else
         Any[sig]
     end