Update the Node.js version on the bots

[Snuffleupagus]

In PR #16293 we increased the minimum supported Node.js version to 18, which is the current LTS version.
After that landed I noticed in the logs, see below, that the bots run older Node.js versions and that could become a problem (as we start using modern JS features).

@calixteman Can you please update the bots to Node.js version 18?

• The Linux-bot now logs (at the start):

npm WARN EBADENGINE Unsupported engine {
npm WARN EBADENGINE   package: undefined,
npm WARN EBADENGINE   required: { node: '>=18' },
npm WARN EBADENGINE   current: { node: 'v16.16.0', npm: '8.11.0' }
npm WARN EBADENGINE }
...

• The Windows-bot now logs (at the start):

npm WARN config global `--global`, `--local` are deprecated. Use `--location=global` instead.
npm WARN EBADENGINE Unsupported engine {
npm WARN EBADENGINE   package: undefined,
npm WARN EBADENGINE   required: { node: '>=18' },
npm WARN EBADENGINE   current: { node: 'v16.16.0', npm: '8.14.0' }
npm WARN EBADENGINE }
...

[calixteman]

I updated node on the windows bot and it should be ok.
For the linux one, ubuntu version was too old (16.04), hence I began to upgrade it: so wait and see now.

[calixteman]

Both bots are now using node 18.16.
I just triggered some tests:
#16397 (comment)

Likely we'll have some diffs on the linux bot: all the packages (and especially font ones) have been updated, hence I wouldn't surprised to see some differences.

[Snuffleupagus]

Seems to work; thank you!