Add explicit CMake version check in case of Gadgetron testing ON

[paskino]

Adds an explicit check of CMake version and message(FATAL_ERROR) if CMake version is below 3.23.

Closes #823

[KrisThielemans]

The job is going through, but that'll be because CMake is more recent presumably, so you can just as well keep an job with the testing on.

To test if the lines are ok, I guess you'll need an older CMake...

[KrisThielemans]

confirmed with CMake 3.10

Make Error at SuperBuild/External_Gadgetron.cmake:141 (message):
  You need at least CMake 3.23 to build Gadgetron tests.

[KrisThielemans]

sadly unrelated error https://github.com/SyneRBI/SIRF-SuperBuild/actions/runs/7740032215/job/21104114360?pr=854#step:8:9340

CMake Error at /home/runner/work/SIRF-SuperBuild/SIRF-SuperBuild/build/builds/ROOT/build/TBB-prefix/src/TBB-stamp/TBB-build-Release.cmake:49 (message):
  Command failed: 2

   'make' 'compiler=gcc' 'cpp0x=1' 'CXXFLAGS= -mno-rtm' 'CPLUS=/usr/lib/ccache/g++-11' 'CONLY=/usr/lib/ccache/gcc-11' 'LDFLAGS='
  See also
    /home/runner/work/SIRF-SuperBuild/SIRF-SuperBuild/build/builds/ROOT/build/TBB-prefix/src/TBB-stamp/TBB-build-*.log

No idea about that.

As it's unrelated, I vote for merging this PR anyway, after cleaning up the jobs.