src: fix -Wsign-compare warnings

This commit addresses the following compilation warnings:

../src/node_crypto.cc:5053:3: warning: comparison of integers
of different signs: 'unsigned int' and 'int' [-Wsign-compare]
  CHECK_EQ(n, BN_bn2binpad(r, data, n));

../src/node_crypto.cc:5054:3: warning: comparison of integers
of different signs: 'unsigned int' and 'int' [-Wsign-compare]
  CHECK_EQ(n, BN_bn2binpad(s, data + n, n));

PR-URL: https://github.com/nodejs/node/pull/30565


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>