[ci deps] Bump node to 20

Summary:
CI tests using nodejs are currently run in node 16. Cashtab is now on node 20.

Other apps that have not yet migrated to node 20 need to do so, as node 16 is past end of life.

So, if this ends up causing issues with other node projects -- they will need to be udpated to accomodate this version.

Test Plan:
./contrib/teamcity/build-configurations.py cashtab-tests

can also run

wget https://deb.nodesource.com/setup_20.x > nodesetup.sh
echo "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 nodesetup.sh" | sha256sum -c

locally, confirm output nodesetup.sh: OK

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15434