fix includes #6441

Author: waruqi

xmake/core/base/interpreter.lua

@@ -1793,7 +1793,7 @@ function interpreter:api_builtin_includes(...)
                 files = os.files(subpath)
             else
                 -- @see https://github.com/xmake-io/xmake/issues/6026
-                files = os.files(path.join(subpath, path.filename(curfile)))
+                files = os.files(path.join(subpath, "xmake.lua"))
             end
             if files and #files > 0 then
                 table.join2(subpaths_matched, files)