Improve test_zeroize.gdb breakpoint

Improve the position of the breakpoint to be set at a line of code that
is less likely to be optimised out by the compiler. Setting the breakpoint
at a place that can be easily optimised out by the compiler will cause the
gdb script to fail as it cannot match the source code line to the
compiled code. For this reason the breakpoint is now set at the fclose()
call which is very unlikely to be optimised out or there might be a
resource leak.
diff --git a/tests/scripts/test_zeroize.gdb b/tests/scripts/test_zeroize.gdb
index 15b8b09..e0b1ac5 100644
--- a/tests/scripts/test_zeroize.gdb
+++ b/tests/scripts/test_zeroize.gdb
@@ -17,7 +17,7 @@
 
 set confirm off
 file ./programs/test/zeroize
-break zeroize.c:90
+break zeroize.c:88
 
 set args ./programs/test/zeroize.c
 run