patch 8.2.3516: terminal window does not have transparent background

Problem:    Terminal window does not have transparent background when
            'termguicolors' is used.
Solution:   Fix the background color. (closes #2361, closes #9002)

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3516,
 /**/
     3515,
 /**/