chore!: Change supported Node from 18 to 20

[Artur-]

Node 20 is the active LTS version for Node.

Node 18 will be end of life soon and new libraries like React 19 support Node 20+

[github-actions]

Test Results

1 158 files  ±0  1 158 suites  ±0   1h 34m 17s ⏱️ + 7m 40s
7 520 tests ±0  7 467 ✅ ±0  53 💤 ±0  0 ❌ ±0 
7 874 runs  +7  7 812 ✅ +7  62 💤 ±0  0 ❌ ±0 

Results for commit 4b79f00. ± Comparison against base commit a784ea1.

♻️ This comment has been updated with latest results.

[sonarqubecloud]

Quality Gate passed

Issues
101 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[vaadin-bot]

This ticket/PR has been released with Vaadin 24.7.0.rc2 and is also targeting the upcoming stable 24.7.0 version.

[PhilippWendler]

Is it intended that this raised the required NPM version from 8.6 to 9.6 and not to something like 9.0?

Also I note that https://vaadin.com/docs/latest/compatibility still lists Node 18.

[mshabarov]

@PhilippWendler thanks for the comment!

About npm 9.0 I'm not sure. Node 20.0 was shipped with npm 9.6, 9.0 may work, but I'd stick with 9.6.
Here is the update for compatibility page vaadin/docs#4257.