update Flax to version 0.9.0

PiperOrigin-RevId: 668047408

Author: Cristian Garcia

README.md

@@ -199,8 +199,8 @@ To cite this repository:
   author = {Jonathan Heek and Anselm Levskaya and Avital Oliver and Marvin Ritter and Bertrand Rondepierre and Andreas Steiner and Marc van {Z}ee},
   title = {{F}lax: A neural network library and ecosystem for {JAX}},
   url = {http://github.com/google/flax},
-  version = {0.8.6},
-  year = {2023},
+  version = {0.9.0},
+  year = {2024},
 }
 ```
 

flax/version.py

@@ -13,4 +13,4 @@
 # limitations under the License.
 
 """Current Flax version at head on Github."""
-__version__ = '0.8.6'
+__version__ = '0.9.0'