bug#65156: 29.1; Reading from pipe with --insert or insert-file-contents no longer supported

[Po Lu]

Mattias Engdegård <mattias.engdegard@gmail.com> writes:

> The current (4767f5eaee) code on emacs-29 fails fileio-tests with:
>
> Test fileio-tests--non-regular-insert condition:
>     (ert-test-failed
>      ((should-error
>        (insert-file-contents "/dev/urandom" nil 5 10))
>       :form
>       (insert-file-contents "/dev/urandom" nil 5 10)
>       :value
>       ("/dev/urandom" 5)
>       :fail-reason "did not signal an error"))

Right, but that's a problem with the test: /dev/urandom is seekable
under the Linux kernel.  I fixed this on master by checking for a
regular file instead of a seekable file when verifying BEG, but that's
too extensive a change for Emacs 29.