[5.8] Fixed cache repository setMultiple with an iterator

[GrahamCampbell]

The Psr\SimpleCache\CacheInterface interface we implement says that an arbitrary iterable can be passed to setMultiple, thus we need to convert it to an array before we pass it to putMany.

---

Without this fix, the following error will occur it something iterable that's not an array is used:

TypeError: Argument 1 passed to Illuminate\Cache\Repository::putMany() must be of the type array, object given, called in /data/src/Illuminate/Cache/Repository.php on line 232

/data/src/Illuminate/Cache/Repository.php:216
/data/src/Illuminate/Cache/Repository.php:232