Fix memory leak if sk_push fails

[ndossche]

If it fails, then the duplicated item is not freed. Solve it by making sure the push cannot fail by reserving the necessary stack size upfront.

Example Valgrind trace:

14,009 (384 direct, 13,625 indirect) bytes in 1 blocks are definitely lost in loss record 27,287 of 27,373
  malloc (at /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
  CRYPTO_zalloc (at /usr/lib/x86_64-linux-gnu/libcrypto.so.3)
  <unknown stack frame>
  ASN1_item_new (at /usr/lib/x86_64-linux-gnu/libcrypto.so.3)
 *ossl_x509_alloc (ossl_x509cert.c:97)
  <unknown stack frame>
  rb_class_new_instance_pass_kw (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  rb_vm_exec (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  rb_catch_obj (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  rb_vm_exec (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_yield (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_ary_each (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  rb_vm_exec (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_yield (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_ary_each (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  rb_vm_exec (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_yield (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_ary_each (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  rb_vm_exec (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_yield (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  rb_ary_each (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  rb_vm_exec (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  rb_catch_obj (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)
  <unknown stack frame>
  <unknown stack frame>
  <unknown stack frame>
  rb_vm_exec (at /usr/lib/x86_64-linux-gnu/libruby-3.2.so.3.2.3)

This was found by a hybrid static-dynamic analyser that looks for inconsistent handling of error checks in bindings.

[ndossche]

Unfortunately because of libressl we cannot use new_reserve and therefore need to check the return value of the push...