Fix line break in deprecation warning

cmake/modules/DuneAddLibrary.cmake

@@ -187,8 +187,9 @@ function(dune_add_library_normal _name)
       message(DEPRECATION
         "The function dune_add_library(<lib> ...) now requires to provide NO_EXPORT or EXPORT_NAME. "
         "We recommend to choose an export name with a camel title case matching your library name "
-        "(e.g., Common, ISTL, and MultiDomainGrid will be exported as Dune::Common, Dune::ISTL, and Dune::MultiDomainGrid) "
-        " * Calls to `dune_add_library(<lib> ...)` without export specification will be supported until Dune 2.11"
+        "(e.g., Common, ISTL, and MultiDomainGrid will be exported as Dune::Common, Dune::ISTL, and Dune::MultiDomainGrid)\n"
+        " * Calls to `dune_add_library(<lib> ...)` without export specification will be supported until Dune 2.11\n"
+
         " * Consumption of unscoped targets `<lib>` will be supported until Dune 2.12")
       set(ARG_EXPORT_NAME ${_name})
     endif()
@@ -245,8 +246,8 @@ function(dune_add_library_interface _name)
       message(DEPRECATION
         "The function dune_add_library(<lib> ...) now requires to provide NO_EXPORT or EXPORT_NAME. "
         "We recommend to choose an export name with a camel title case matching your library name "
-        "(e.g., Common, ISTL, and MultiDomainGrid will be exported as Dune::Common, Dune::ISTL, and Dune::MultiDomainGrid) "
-        " * Calls to `dune_add_library(<lib> ...)` without export specification will be supported until Dune 2.11"
+        "(e.g., Common, ISTL, and MultiDomainGrid will be exported as Dune::Common, Dune::ISTL, and Dune::MultiDomainGrid)\n"
+        " * Calls to `dune_add_library(<lib> ...)` without export specification will be supported until Dune 2.11\n"
         " * Consumption of unscoped targets `<lib>` will be supported until Dune 2.12")
       set(ARG_EXPORT_NAME ${_name})
     endif()