patch 8.2.5061: C89 requires signal handlers to return void

Problem:    C89 requires signal handlers to return void.
Solution:   Drop RETSIGTYPE and hard-code a void return value.
diff --git a/src/version.c b/src/version.c
index a361f9c..074652b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -735,6 +735,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    5061,
+/**/
     5060,
 /**/
     5059,