Recent change for callables in model factories attributes breaks existing factories

[Crinsane]

• Laravel Version: 5.4.34
• PHP Version: 7.0.8
• Database Driver & Version: SQL server

Description:

The recent change to add support for callables in model factories attributes broke our testsuite. #20692
I filtered the problem down to the change made in this commit 91765f5 where it checks if the attribute you give the factory is a callable.
In one of our factories, a possible value of an attribute is DIR, and it PHP will tell you this is callable (the dir() global function). So it will try to call dir() and pass it the attributes array, which will result in an exception: dir() expects parameter 1 to be a valid path, array given

Steps To Reproduce:

1. Create a model factory
2. Set one of the attributes to some global function name
3. Try to use the factory and see it fail

[themsaid]

fixed

[Crinsane]

Thanks a lot!