patch 8.1.1853: timers test is still flaky

Problem:    Timers test is still flaky.
Solution:   Compute the time to sleep more accurately.
diff --git a/src/version.c b/src/version.c
index abbb3b0..38290c6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1853,
+/**/
     1852,
 /**/
     1851,