From 'assertEquals' to 'assertSame'

After discovering this bite (40e06d1b5952bb8d30b4c6ca9ee06352870e1ced) from the _type juggling_ I propose to switch assertions on the Generators (especially in shrink/1 tests) from `assertEquals` to `assertSame`.
Even if type juggling is a PHP feature, types matters for us. :-)