ENH: Bump elastix version to 2023-07-19, inc. SetInitialTransform

Follow-up to #211
commit 1043f10 "ENH: Bump elastix version to
2023-05-15, use C++17"

Including:

  SuperElastix/elastix#936
  SuperElastix/elastix@115d8e1
  ENH: Add `ElastixRegistrationMethod::SetInitialTransform

  SuperElastix/elastix#933
  SuperElastix/elastix@d33a0d5
  BUG: Fix reference count in ConvertItkTransformBaseToSingleItkTransform

  SuperElastix/elastix#924
  SuperElastix/elastix@71a4a9a
  ENH: Add TransformParameterFileName property to TransformixFilter

  SuperElastix/elastix#922
  SuperElastix/elastix@9d76b86
  ENH: Restore ELASTIX_BUILD_EXECUTABLE CMake option

  SuperElastix/elastix#909
  SuperElastix/elastix@9e64269
  ENH: ElastixRegistrationMethod writes initial transform parameter files

  SuperElastix/elastix#903
  SuperElastix/elastix@2170592
  ENH: Remove the letter 's' from "InitialTransformParametersFileName"

  SuperElastix/elastix#898
  SuperElastix/elastix@691c358
  BUG: Add InitialTransformParameterObject maps to registration result

CMakeLists.txt

@@ -56,7 +56,7 @@ if(SKBUILD)
 endif()
 
 set(elastix_GIT_REPOSITORY "https://github.com/SuperElastix/elastix.git")
-set(elastix_GIT_TAG "b9b8e20aef83f94ed38a81cc38625a1bfddf1053")
+set(elastix_GIT_TAG "115d8e1c7b0b23973bfc919a2bf4768f32e4e843")
 FetchContent_Declare(
   elx
   GIT_REPOSITORY ${elastix_GIT_REPOSITORY}