Only install tests data for prefix builds

If we install tests data for non-prefix builds it can cause tests to
fail as they find the data in the wrong location. An example of this is
tst_qsslkey.

Change-Id: I55bd2ff4cb5a0857dc857cb2149ffe4436ec6f99
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtBuild.cmake

@@ -2797,11 +2797,11 @@ function(qt_add_test name)
         foreach(testdata IN LISTS arg_TESTDATA)
             set(testdata "${CMAKE_CURRENT_SOURCE_DIR}/${testdata}")
             if (IS_DIRECTORY "${testdata}")
-                qt_copy_or_install(
+                qt_install(
                     DIRECTORY "${testdata}"
                     DESTINATION "${testdata_install_dir}")
             else()
-                qt_copy_or_install(
+                qt_install(
                     FILES "${testdata}"
                     DESTINATION "${testdata_install_dir}")
             endif()