Kernel prepatch 6.18-rc7

Linus has released 6.18-rc7, probably the
last -rc before the 6.18 release.

So the rc6 kernel wasn't great: we had a last-minute core VM
regression that caused people problems.

That's not a great thing late in the release cycle like that, but
it was a fairly trivial fix, and the cause wasn't some horrid bug,
just a latent gotcha that happened to then bite a late VM fix. So
while not great, it also doesn't make me worry about the state of
6.18. We're still on track for a final release next weekend unless
some big new problem rears its ugly head.