patch 9.1.0820: tests: Mac OS tests are too flaky

Problem:  tests: Mac OS tests are too flaky
Solution: Increase max test timeout to 25 minutes,
          allow up to 10 retries on Mac OS runners,
          refactor runtest.vim (Milly).

closes: #15940

Co-authored-by: K.Takata <kentkt@csc.jp>
Signed-off-by: Milly <milly.ca@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 838f25a..e042965 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    820,
+/**/
     819,
 /**/
     818,