10% speedup due to loadstring fallback check

[westurner]

In src/jest-runtime/src/init.lua

• From the commit logs of Roblox/jest-roblox:
  https://github.com/Roblox/jest-roblox/commits/master/

  • Apply "Fix test runtime regression due to loadstring fallback check"
    Roblox@74399db

• jest-lua/src/jest-runtime/src/init.lua

  Line 1958 in a5d089a

  moduleFunction = loadstring(modulePath.Source, modulePath:GetFullName())