Don't add a colon after mentioning someone

### Your use case

#### What would you like to do?
Mention a user without a semicolon ( : ) being added after their name.

#### Why would you like to do it?
We use Matrix for communication in a small project. I sometimes mention people in a message like "I had a call with @Peter and @Pan. Here's some notes, let me know if I missed anything."

In that case the message is directed to everyone and names appear in the middle of a sentence rather than at the beginning. Therefore I have to remove the semicolon that gets added after each mention/tagged user.

#### How would you like to achieve it?
n/a

### Have you considered any alternatives?

Having a space only is fine.

### Additional context

_No response_

### Are you willing to provide a PR?

Yes, but I don't have the skills so I can't :-)

No file, test, or entry point is named in the issue. Locate the mention formatting path in the relevant Element client, then verify with coverage for mentions in mid-sentence and confirm that a mention is followed by a space rather than a colon.

Written by the indexing model from the issue text.