Add test for `hk.initialisers.Constant(list)`.
Add test for `hk.initialisers.Constant(list)`.

While not technically supported (per the types on the ctor) some users are
relying on this so we are adding tests to defend existing behaviour ahead of
google/jax#7737 being resolved in Haiku via deepmind/dm-haiku#324.

PiperOrigin-RevId: 432897736

deepmind/dm-haiku,deepmind/dm-haiku