CRYPTO_mem_debug_push() and CRYPTO_mem_debug_pop() should return 0

Those 2 functions historically only ever returned 0 or 1. In OpenSSL 3.0
they were made no-ops and the documentation says they always return 0. In
fact they were returning -1. If any application was actually using these
functions then it may appear that they were actually successful (e.g. -1
could be interpreted as "true").

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #18967)

(cherry picked from commit f868454)

crypto/mem.c

@@ -285,12 +285,12 @@ int CRYPTO_set_mem_debug(int flag)
 int CRYPTO_mem_debug_push(const char *info, const char *file, int line)
 {
     (void)info; (void)file; (void)line;
-    return -1;
+    return 0;
 }
 
 int CRYPTO_mem_debug_pop(void)
 {
-    return -1;
+    return 0;
 }
 
 void CRYPTO_mem_debug_malloc(void *addr, size_t num, int flag,