ENH: Bump Python package version to 0.21.0

Author: thewtex

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "scikit_build_core.build"
 
 [project]
 name = "itk-elastix"
-version = "0.20.0"
+version = "0.21.0"
 description = "Provides an ITK Python interface to elastix, a toolbox for rigid and nonrigid registration of images"
 readme = "README.md"
 license = {file = "LICENSE"}