RFR: 2141: Inform user about accepting fork repo invite in /backport command reply

[Zhao Song]

On Thu, 11 Jan 2024 20:30:47 GMT, Zhao Song <zsong at openjdk.org> wrote:

> After users issued /backport command to create backport PRs in GitHub, skara bot will invite the users to be collaborators of the bot's fork. Sometimes, the users will ignore the invitation and later when they are trying to update the backport branch, they will find they don't have the access. This patch is trying to add a comment to remind the user to accept the invitation.

bots/pr/src/main/java/org/openjdk/skara/bots/pr/BackportCommand.java line 416:

> 414:                 reply.print("@");
> 415:                 reply.print(realUser.username());
> 416:                 reply.print(" ");

If the backport command was used in a pull request, in the beginning of the reply message, the bot will @`the author of the pull request` and @`the command issuer`. 
To be clear, I would like to @`the command issuer` again before the reminder.

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PR Review Comment: https://git.openjdk.org/skara/pull/1598#discussion_r1449366891