Use only bits types for CONTAINER_TYPES

A change introduced in Julia 0.7 made BigInt a subtype of Signed. The
change resulted in the code including BigInt in the CONTAINER_TYPES
which resulted in an exceptions since BigInt is not a bits type.

JuliaLang/julia#23473

Author: omus

test/runtests.jl

@@ -17,7 +17,7 @@ const FD4 = FixedDecimal{Int, 4}
 const WFD2 = FixedDecimal{Int128, 2}
 const WFD4 = FixedDecimal{Int128, 4}
 
-const CONTAINER_TYPES = [subtypes(Signed); subtypes(Unsigned)]
+const CONTAINER_TYPES = Base.BitInteger_types  # Integer concrete subtypes which are bits
 
 # these arrays should be kept sorted manually
 const keyvalues = Dict(