patch 7.4.993

Problem:    Test 87 is flaky on AppVeyor.
Solution:   Reduce the minimum background thread count.

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    993,
 /**/
     992,
 /**/