[bullseye-deps] Install nodejs 16 instead of 15

Summary:
T3044

CI tests are failing for D13677 because CI is using nodejs 15 instead of 16

CONTRIBUTING.md already is referencing nodejs 16

Test Plan: ...I'm not sure how to test this or if I've implemented this in the right place

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13686