fix: strict check for collapse item heading attribute

[rivanuff]

[Copilot]

Pull request overview

This PR addresses block validation issues in the deprecated Collapse Item block by handling cases where the heading attribute is missing (null/undefined) more strictly during save.

Changes:

• Update collapse-item save output to avoid rendering an invalid heading wrapper when heading is null/undefined.
• Add a new deprecated collapse-item version intended to prevent validation failures for content affected by an undefined heading.
• Minor JS simplification in the deprecated greetings inspector.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/deprecated/gemeenten/src/blocks/greetings/inspector.js	Simplifies state update using object property shorthand.
packages/deprecated/core/src/collapse/collapse-item/save.js	Treats heading null/undefined the same as an empty heading (no wrapper).
packages/deprecated/core/src/collapse/collapse-item/deprecated.js	Adds a deprecated block version to handle validation when heading is undefined.
package-lock.json	Updates lockfile entries (notably removing libc constraints for several optional native packages).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.