test: suppress compiler warning in test_bigint

Currently the are two of following compiler warnings is
generated:

In file included from ../test_bigint.c:5:
../test_bigint.c: In function ‘CreateTooBigBigInt’:
../test_bigint.c:120:22: warning:
‘words’ may be used uninitialized [-Wmaybe-uninitialized]

This commit initialized the words array to avoid these warnings.

PR-URL: https://github.com/nodejs/node/pull/40253


Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>