Remove Base.Callable type restriction on func argument

Base.Callable doesn't actually mean everything that can be called. It's a union of Function and type. We don't need this restriction in our case.

Author: NHDaly

src/MultiThreadedCaches.jl

@@ -119,7 +119,7 @@ end
 
 const CACHE_MISS = :__MultiThreadedCaches_key_not_found__
 
-function Base.get!(func::Base.Callable, cache::MultiThreadedCache{K,V}, key) where {K,V}
+function Base.get!(func, cache::MultiThreadedCache{K,V}, key) where {K,V}
     # If the thread-local cache has the value, we can return immediately.
     # We store tcache in a local variable, so that even if the Task migrates Threads, we are
     # still operating on the same initial cache object.