Require Node@20

[nikku]

Proposed Changes

Update the requirement for node to Node@20. This is soon the legacy node version, so I think lifting up our requirements is fine.

At this stage this will simply indicate the incompatibility when upgrading bpmnlint. It will still work on node@16, though we don't guarantee it anymore, going into the future.

Checklist

To ensure you provided everything we need to look at your PR:

• Brief textual description of the changes present
• Visual demo attached
• Steps to try out present, i.e. using the @bpmn-io/sr tool
• Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}

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Additional context:

• Internally, for development, we already use Node@20 for a long time
• Certain upgrades, such as migrating from the now unmaintained eslint@8 to @9 require us also to upgrade to node@20