Version bump to 0.6.2 (#1252)

I'll do the cherry picks soon for an 0.6.2 release that will fix
mixed precision support on keras-core. This is just the version bump.

Author: mattdangerw

keras_nlp/__init__.py

@@ -28,4 +28,4 @@
 from keras_nlp import utils
 
 # This is the global source of truth for the version number.
-__version__ = "0.6.2.dev0"
+__version__ = "0.6.2"