patch 9.0.0053: E1281 not tested with the old regexp engine

Problem:    E1281 not tested with the old regexp engine.
Solution:   Loop over the values of 'regexp'. (Dominique Pellé, closes #10695)
diff --git a/src/version.c b/src/version.c
index 3c4e96c..9e7a988 100644
--- a/src/version.c
+++ b/src/version.c
@@ -736,6 +736,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    53,
+/**/
     52,
 /**/
     51,