Chex release 0.1.88

https://github.com/google-deepmind/chex/releases

Fix test_assert_trees_all_equal_prng_keys by @copybara-service in #366
Avoid relying on jax.lib.xla_bridge._backends, as this is private and will soon be deleted by @copybara-service in #367
Release 0.1.88. by @copybara-service in #369

Full changelog: v0.1.87…v0.1.88