Build Error: Can't find Ruby (MacOS)

[leopold-franz]

1. Error message (copy & pasted) and focused description of the problem.

[ 72%] Completed 'Elastix'
[ 77%] Built target Elastix
[ 79%] Performing configure step for 'SimpleITK'
Not searching for unused variables given on the command line.
loading initial cache file /Users/lfranz/Desktop/tracking/sitk/build/SimpleITK-build/CMakeCacheInit.txt
-- Building SimpleITK version "2.0.0rc2.dev910-ga138e"
CMake Error at /usr/local/Cellar/cmake/3.22.2/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find Ruby (missing: Ruby_EXECUTABLE Ruby_LIBRARY) (found suitable
  version "2.6.3", minimum required is "1.8.0")
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.22.2/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE)
  /usr/local/Cellar/cmake/3.22.2/share/cmake/Modules/FindRuby.cmake:488 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  CMake/sitkLanguageOptions.cmake:236 (find_package)
  CMakeLists.txt:353 (include)


-- Configuring incomplete, errors occurred!
See also "/Users/lfranz/Desktop/tracking/sitk/build/SimpleITK-build/CMakeFiles/CMakeOutput.log".
See also "/Users/lfranz/Desktop/tracking/sitk/build/SimpleITK-build/CMakeFiles/CMakeError.log".
make[2]: *** [SimpleITK-prefix/src/SimpleITK-stamp/SimpleITK-configure] Error 1
make[1]: *** [CMakeFiles/SimpleITK.dir/all] Error 2
make: *** [all] Error 2

It seems that there is an error with my Ruby version.
Here is my Ruby version:

ruby -v
ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.x86_64-darwin19]

2. Operating system, and version (e.g. OSX 10.11.6): MacOS Catalina 10.15.7
3. Programming language, and version (e.g. Python 2.7.14, R 3.2.3): Python 3.8.8
4. How did you install SimpleElastix: I am building simpleelastix according to https://simpleelastix.readthedocs.io/GettingStarted.html#compiling-on-mac-os-x.