Clarification of invite->knock introduced in 1.10 should be at least a warning on older rendered spec versions

Nobody has claimed this yet.

**Link to problem area**:

- The files touched in https://github.com/matrix-org/matrix-spec/issues/1717

**Issue**

https://github.com/matrix-org/matrix-spec/issues/1717 introduced a change to room versions introduced in earlier spec versions retroactively. While this in general is fine due to the versioning of Spec the Room versions are explicitly building upon their own room version versioning schema. This means that there now are at least Spec 1.9 and Spec 1.10 saying different rules on the room versions 7, 8, 10 and 11.

In normal changes to S-S api or C-S Api updating the spec version would be sufficient. For Room Versions it is not as Matrix spec these days doesnt exist in isolation of the wider internet. Which means some projects like TI-Messenger are pinning their specs on top of specific matrix spec versions instead of running latest at all times. This means anyone relying on 1.9 (or others with the old rules) will now run different room versions than the rest of the ecosystem as these pinnings usually have a statement of "You can use newer spec if they are backwards compatible" (this is what TI-Messenger spec for example said when they pinned to 1.3). However the clarification here is not backwards compatible meaning people would not be using the same room versions as the rest of the ecosystem.

Ideally it would be a good idea to at least add warning boxes to the older affected spec versions that 1.10 had a crucial fix to these versions which should be applied. I do understand that this clarification technically is following process of the way spec versioning goes. But sadly this is somewhat of an edgecase of how room versioning and spec versioning interact with each other and they technically are not moving at the same pace.

Start by comparing the rendered Spec 1.9 and 1.10 content, using issue 1717 and room versions 7, 8, 10, and 11 as the affected scope. Identify how older spec versions are maintained and add warning boxes explaining that the 1.10 clarification should be applied. Done means the affected older renders clearly warn readers about the change.

Written by the indexing model from the issue text.