patch 8.0.0473: no test covering arg_all()

Problem:    No test covering arg_all().
Solution:   Add a test expanding ##.
diff --git a/src/version.c b/src/version.c
index e4a40f2..8237679 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    473,
+/**/
     472,
 /**/
     471,