Replaces a 7.x reference with the `{prev-major-last}` variable, which will use the last minor of the previous major (currently 7.17 for 8.x).
Relates to #70451.
* Implement dedicated client version compatibility
Add further dedicated client (xDBC, CLI) compatibility rules and
document these. A client is version-compatible with the server if:
- it supports version compatibility (past or on 7.7.0); and
- it's not on a version newer than server's; and
- it's major version is at most one unit behind server's.
Co-authored-by: James Rodewig <40268737+jrodewig@users.noreply.github.com>
