win: Set correct folder permissions after folder creation (#38942)

libuv's mkdir does not implement the mode argument on Windows, as a
result the folder mode is never passed on the Windows platform.

Forcibly change the folder permissions to agree with the mode passed
into `mkdir`.

base/file.jl

@@ -179,6 +179,8 @@ function mkdir(path::AbstractString; mode::Integer = 0o777)
             uv_error("mkdir($(repr(path)); mode=0o$(string(mode,base=8)))", ret)
         end
         ccall(:uv_fs_req_cleanup, Cvoid, (Ptr{Cvoid},), req)
+        # mode is not implemented in mkdir in libuv yet, so do it here
+        Sys.iswindows() && chmod(path, mode)
         return path
     finally
         Libc.free(req)