Fix rust-analyzer lint on __info_func__cb

[edman]

The lint message was:

Variable `__info_func__cb` should have snake_case name, e.g. `__info_func_cb`

The message shows up in redis-module dependees when calling the redis_module! macro. You can see it in the examples here too.

Notice the tests weren't fully passing in my machine, I had 5 failures before and after this change. Not sure I did something wrong.