Backport fails for jdk15u-dev

About an hour ago, a user requested a backport for this mainline commit:

https://github.com/openjdk/jdk/commit/f5766287

Since then, the pr bot has been generating errors:

Exception during item execution (CommitCommandWorkItem@openjdk/jdk:f5766287): Request returned bad status: 404

java.lang.RuntimeException: Request returned bad status: 404
at org.openjdk.skara.network/org.openjdk.skara.network.RestRequest.transformBadResponse(RestRequest.java:309)
at org.openjdk.skara.network/org.openjdk.skara.network.RestRequest.execute(RestRequest.java:385)
at org.openjdk.skara.network/org.openjdk.skara.network.RestRequest$QueryBuilder.execute(RestRequest.java:180)
at org.openjdk.skara.forge/org.openjdk.skara.forge.github.GitHubRepository.canPush(GitHubRepository.java:544)
at org.openjdk.skara.bots.pr/org.openjdk.skara.bots.pr.BackportCommand.handle(BackportCommand.java:162)
at org.openjdk.skara.bots.pr/org.openjdk.skara.bots.pr.CommitCommandWorkItem.processCommand(CommitCommandWorkItem.java:131)
at org.openjdk.skara.bots.pr/org.openjdk.skara.bots.pr.CommitCommandWorkItem.run(CommitCommandWorkItem.java:171)
at org.openjdk.skara.bot/org.openjdk.skara.bot.BotRunner$RunnableWorkItem.run(BotRunner.java:84)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:831)