[!759] add missing file FindQuadMath.cmake to CMakeLists.txt

Merge branch 'issue/add_missing_install_file_quadmath' into 'master'

ref:core/dune-common Maybe this MR could also be cherry-picked into the
releases/2.7 branch

See merge request [!759]

  [!759]: gitlab.dune-project.org/core/dune-common/merge_requests/759

cmake/modules/CMakeLists.txt

@@ -38,6 +38,7 @@ install(FILES
   FindMProtect.cmake
   FindParMETIS.cmake
   FindPTScotch.cmake
+  FindQuadMath.cmake
   FindSphinx.cmake
   FindSuiteSparse.cmake
   FindTBB.cmake