patch 9.0.0668: CI on Mac M1 only uses clang

Problem:    CI on Mac M1 only uses clang
Solution:   Also run with gcc. (closes #11263)
diff --git a/src/version.c b/src/version.c
index 0d3e911..b7bb569 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    668,
+/**/
     667,
 /**/
     666,