Need Node.js 16.15.0 and Ruby 2.7.6

What does this Merge Request do and why?

This MR updates the .tool-versions file to match new Node.js and Ruby versions.

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.

Closes #1522 (closed)