`mkdir_on_file` fails on 6.1.0

When a file is a replaced with a directory, we get EIO on Linux 6.1.0. Could just be the old kernel version.

Three tests fail---`summary.sh`, `all-commit-cases.sh`, and `mkdir_on_file.sh`. But it's all the same error. Symptoms look like:

```
Running all-commit-cases.sh... FAIL (3)
=======
STDOUT:
=======
Case 3:
=======

=======
STDERR:
=======
rm: cannot remove 'olddir': Input/output error
mkdir: cannot create directory ‘olddir’: File exists
rm: cannot remove '/tmp/tmp.YWPnAHSgKG.try-1737994562875/temproot//initrd.img': No such file or directory
rm: cannot remove '/tmp/tmp.YWPnAHSgKG.try-1737994562875/temproot//initrd.img.old': No such file or directory
rm: cannot remove '/tmp/tmp.YWPnAHSgKG.try-1737994562875/temproot//vmlinuz': No such file or directory
rm: cannot remove '/tmp/tmp.YWPnAHSgKG.try-1737994562875/temproot//vmlinuz.old': No such file or directory
rm: cannot remove '/tmp/tmp.rSpDPo9Jek.try-1737994562952/temproot//initrd.img': No such file or directory
rm: cannot remove '/tmp/tmp.rSpDPo9Jek.try-1737994562952/temproot//initrd.img.old': No such file or directory
rm: cannot remove '/tmp/tmp.rSpDPo9Jek.try-1737994562952/temproot//vmlinuz': No such file or directory
rm: cannot remove '/tmp/tmp.rSpDPo9Jek.try-1737994562952/temproot//vmlinuz.old': No such file or directory
mkdir: cannot create directory ‘wasfile’: Input/output error
```