Kernel prepatch 6.19-rc4

The 6.19-rc4 kernel prepatch is out for
testing.

So this rc is still a bit smaller than usual, but it's not _much_
smaller, and I think next week is likely going to be more or less
back to normal.

Which is all exactly as expected, and nothing here looks
particularly odd. I'll make an rc8 this release just because of the
time lost to the holidays, not because it looks like we'd have any
particular issues pending (knock wood).