Fix illogical heading order for the versions list

[ahukkanen]

🎩 What? Why?

The versions list items order is illogical.

Take a look e.g. at this page:
https://meta.decidim.org/processes/roadmap/f/122/proposals/16942/versions

After the "Versions" heading, the heading jumps from h3 -> h6.

WCAG 2.2 / 1.3.1 Info and Relationships (Level A)

https://www.w3.org/TR/WCAG22/#info-and-relationships
https://www.w3.org/WAI/WCAG22/Understanding/info-and-relationships.html

Testing

Give the linked versions page to a visually impaired user and ask them to read it.

📋 Checklist

• ❓ CONSIDER adding a unit test if your PR resolves an issue.
• ✔️ DO check open PR's to avoid duplicates.
• ✔️ DO keep pull requests small so they can be easily reviewed.
• ✔️ DO build locally before pushing.
• ✔️ DO make sure tests pass.
• ✔️ DO make sure any new changes are documented in docs/.
• ✔️ DO add and modify seeds if necessary.
• ✔️ DO add CHANGELOG upgrade notes if required.
• ✔️ DO add to GraphQL API if there are new public fields.
• ✔️ DO add link to MetaDecidim if it's a new feature.
• ❌AVOID breaking the continuous integration build.
• ❌AVOID making significant changes to the overall architecture.

[andreslucena]

Can you please backport to v0.26-stable 🙏🏽? Thanks

[ahukkanen]

Backport at #8950.