Update release notes

RELEASE-NOTES.md

@@ -13,7 +13,7 @@ Instead update the vNext section until 4.0.0 is out.
 ### No-yet working features
 We plan to get these working again, but at this point their inner workings have not been refactored.
 - Timeseries distributions (see [#4642](https://github.com/pymc-devs/pymc/issues/4642))
-- Mixture distributions (see [#4781](https://github.com/pymc-devs/pymc/issues/4781))
+- Nested Mixture distributions (see [#5533](https://github.com/pymc-devs/pymc/issues/5533))
 - Cholesky distributions (see WIP PR [#4784](https://github.com/pymc-devs/pymc/pull/4784))
 - Variational inference submodule (see WIP PR [#4582](https://github.com/pymc-devs/pymc/pull/4582))
 - Elliptical slice sampling (see [#5137](https://github.com/pymc-devs/pymc/issues/5137))
@@ -74,6 +74,7 @@ All of the above apply to:
   - In the gp.utils file, the `kmeans_inducing_points` function now passes through `kmeans_kwargs` to scipy's k-means function.
   - The function `replace_with_values` function has been added to `gp.utils`.
   - `MarginalSparse` has been renamed `MarginalApprox`.
+  - Removed `MixtureSameFamily`. `Mixture` is now capable of handling batched multivariate components (see [#5438](https://github.com/pymc-devs/pymc/pull/5438)).
 - ...
 
 ### Expected breaks