[ci] Set r=ON globally to see where we stand with R

Author: guitargeek

.github/workflows/root-ci-config/buildconfig/global.txt

@@ -70,7 +70,7 @@ opengl=ON
 pyroot=ON
 pythia8=OFF
 qt6web=OFF
-r=OFF
+r=ON
 roofit=ON
 roofit_multiprocess=ON
 root7=ON