cmake: fix to use variable for the curl namespace

Replace (wrong) literal with a variable to specify the curl
namespace.

Follow-up to 1199308dbc #11505

Reported-by: balikalina on Github
Fixes 1199308dbc (r123923098)
Closes #11629

CMake/curl-config.cmake.in

@@ -35,4 +35,4 @@ include("${CMAKE_CURRENT_LIST_DIR}/@TARGETS_EXPORT_NAME@.cmake")
 check_required_components("@PROJECT_NAME@")
 
 # Alias for either shared or static library
-add_library(curl::libcurl ALIAS curl::@LIB_SELECTED@)
+add_library(@PROJECT_NAME@::libcurl ALIAS @PROJECT_NAME@::@LIB_SELECTED@)