cleanup: Disallow stack frames of over 9000 bytes.

This only happens in tests, which are easy to fix. Inside toxcore we
should actually be more stringent, but for now this helps already.

.github/scripts/flags-gcc.sh

@@ -18,7 +18,7 @@ add_flag -Wenum-compare
 add_flag -Wfloat-equal
 add_flag -Wformat=2
 add_flag -Wframe-address
-add_flag -Wframe-larger-than=12400
+add_flag -Wframe-larger-than=9000
 add_flag -Wignored-attributes
 add_flag -Wignored-qualifiers
 add_flag -Winit-self