patch 9.0.0763: MS-Windows: warning for using int for size_t

Problem:    MS-Windows: warning for using int for size_t.
Solution:   Declare variable as size_t.
diff --git a/src/time.c b/src/time.c
index a5be297..a7daaf1 100644
--- a/src/time.c
+++ b/src/time.c
@@ -1123,7 +1123,7 @@
 #ifdef HAVE_STRFTIME
     struct tm	tmval;
     struct tm	*curtime;
-    int		n;
+    size_t	n;
 
     if (vim_time() - tt >= 100)
     {