RFR: 1686: Warning message for backport mistakes is not clear [v3]

[Magnus Ihse Bursie]

On Tue, 22 Nov 2022 21:38:40 GMT, Zhao Song <zsong at openjdk.org> wrote:

>> A user reported that he found many PR with "issue is not open" warning. After discussing in slack, we found that this happens because backport-style PR wasn't used. 
>> 
>> To improve the experience of user, we need to give some useful information to the user instead of just telling them "Issue is not open".
>> 
>> In this patch, when a user is trying to create a PR related with a resolved issue, we will assume that the user wants to create a backport PR but in the wrong way. So in this case, we will tell the user how to create a correct backport pr. In other case, for example, the issue is closed with "Not an Issue", we will still just tell the user "Issue is not open".
>
> Zhao Song has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update test

LGTM

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Marked as reviewed by ihse (Reviewer).

PR: https://git.openjdk.org/skara/pull/1425