Update Group Notes' template to use another stability sentence by default.

[jennyliang220]

Some background

The new TR template is adding an alternative sentence for Note track documents.

For (Draft) Notes, allow both sentence in SoTD:

1. This Group (Draft )?Note is endorsed by the XXX Group, but is not endorsed by W3C itself nor its Members.

2. Group (Draft )?Notes are not endorsed by W3C nor its Members.

Specberus/Pubrules has implemented this rule in https://github.com/w3c/specberus/pull/1707/files#diff-a103640e2cfd35023ed7a864aa7fa0b254a9d3515b5b26e900b113d0601b60d1, now it recognizes both sentences.

New requirements for Respec

As @fantasai mentioned in w3c/specberus#1705 (comment), for Notes, please use:

This Group Note is endorsed by the XXX Group, but is not endorsed by W3C itself nor its Members.