tests/bsim: Switch main return type from void to int

These changes were automated using coccinelle with the following
script:

@@
@@
- void
+ int
main(...) {
    ...
-	return;
+	return 0;
    ...
}

Signed-off-by: Keith Packard <keithp@keithp.com>

tests/bsim/bluetooth/host/gatt/settings/src/main.c

@@ -89,9 +89,10 @@ static struct bst_test_list *install(struct bst_test_list *tests)
 
 bst_test_install_t test_installers[] = { install, NULL };
 
-void main(void)
+int main(void)
 {
 	bst_main();
+	return 0;
 }