FindMatlab: Add R2021b => 9.11 version

R2021b released 09/22/2021.

Modules/FindMatlab.cmake

@@ -261,6 +261,7 @@ if(NOT MATLAB_ADDITIONAL_VERSIONS)
 endif()
 
 set(MATLAB_VERSIONS_MAPPING
+  "R2021b=9.11"
   "R2021a=9.10"
   "R2020b=9.9"
   "R2020a=9.8"