lint: port test items diagnostics

Signed-off-by: David Wood <david.wood@huawei.com>

Author: davidtwco

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -371,3 +371,5 @@ lint-builtin-trivial-bounds = {$predicate_kind_name} bound {$predicate} does not
 
 lint-builtin-ellipsis-inclusive-range-patterns = `...` range patterns are deprecated
     .suggestion = use `..=` for an inclusive range
+
+lint-builtin-unnameable-test-items = cannot test inner items

compiler/rustc_lint/src/builtin.rs

@@ -1915,7 +1915,7 @@ impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
         let attrs = cx.tcx.hir().attrs(it.hir_id());
         if let Some(attr) = cx.sess().find_by_name(attrs, sym::rustc_test_marker) {
             cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
-                lint.build("cannot test inner items").emit();
+                lint.build(fluent::lint::builtin_unnameable_test_items).emit();
             });
         }
     }