Enhancements and bugs should not have multiple fix versions. However, this is not enforced at the moment.

If a backport is created through the /backport command, this will lead to an erroneous backport issue being created for the 'main' fix version.

Here is an example of this: https://bugs.openjdk.org/browse/JDK-8310053 The timeline of this problem is:

- An issue is created with 2 fix versions (21, and 22 in this case)
- A PR is created for this issue
- After the PR is integrated, the /backport jdk21 command is used
- At that point, the bots create a backport issue targeting 22 and close it as resolved/fixed (the use of the /backport command and the integration were only a few minutes apart, so it is not clear which one resulted in the backport issue for 22 being created. Though it seems more likely that it was the integration)
- The backport PR is created, reviewed and integrated
- At that point the bots create a backport issue targeting 21 and close it as resolved/fixed
- The main JBS issue remains open. Luckily both commit messages mention the issue number from the main issue.

It would be helpful if the bot that is responsible for checking that a PR title matches the title of a JBS issue, could also check if an Enhancement or Bug has multiple fix versions, and issue a similar warning in that case.

(Alternatively, the /backport command could be refused if the issue linked to a PR has multiple fix version. But, it might be nice to enforce a single fix version for all PRs, even if they are never backported).