⬆️ Update @node-red-contrib-themes/theme-collection to v3.1.6

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@node-red-contrib-themes/theme-collection	3.1.5 -> 3.1.6

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Release Notes

node-red-contrib-themes/theme-collection (@​node-red-contrib-themes/theme-collection)

### [`v3.1.6`](https://togithub.com/node-red-contrib-themes/theme-collection/releases/tag/3.1.6) [Compare Source](https://togithub.com/node-red-contrib-themes/theme-collection/compare/3.1.5...3.1.6) ### What’s changed #### 🚀 Enhancements - Add support for Mermaid themes ([#​340](https://togithub.com/node-red-contrib-themes/theme-collection/pull/340)) [@​bonanitech](https://togithub.com/bonanitech) #### 📖 Documentation - Add support for Mermaid themes ([#​340](https://togithub.com/node-red-contrib-themes/theme-collection/pull/340)) [@​bonanitech](https://togithub.com/bonanitech) #### ⬆️ Dependency updates

3 changes

- Update fs-extra to v11.2.0 ([#​343](https://togithub.com/node-red-contrib-themes/theme-collection/pull/343)) [@​renovate](https://togithub.com/renovate) - Update dessant/lock-threads action to v5.0.1 ([#​341](https://togithub.com/node-red-contrib-themes/theme-collection/pull/341)) [@​renovate](https://togithub.com/renovate) - Update dessant/lock-threads action to v5 ([#​339](https://togithub.com/node-red-contrib-themes/theme-collection/pull/339)) [@​renovate](https://togithub.com/renovate)

**Full Changelog**: https://github.com/node-red-contrib-themes/theme-collection/compare/3.1.5...3.1.6

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