[5.6] [fix] support tags as variadic params in Repository::tags

[jarektkaczyk]

TaggableStore::tags accepts tags as array or variadic params, but the Repository::tags does not, which makes this happen:

Cache::tags(['foo', 'bar', 'baz']) // works fine:
$this->store->tags(['foo', 'bar', 'baz'])

// but

Cache::tags('foo', 'bar', 'baz') // will pass only first param to the TaggableStore:
$this->store->tags('foo') // wrong!

This PR fixes the bug.