Replace `yes` command by `while-echo` in test `tests/ui/process/process-sigpipe.rs`
The `yes` command is not available on all platforms.
Fixes#108596.
Inviting `@mvf` as he contributed to this patch. Thanks! This issue has been discussed in https://github.com/rust-lang/rust/pull/106673 but was moved to #108596 to get going.
CC `@gh-tr`
r? `@workingjubilee`
`@rustbot` label +O-neutrino
Notes about the comments https://github.com/rust-lang/rust/pull/106673#discussion_r1117324265:
- The `echo` command is `/proc/boot/echo` (not built-in)
- `/bin/sh` is a symlink to `/proc/boot/ksh`
```sh
# ls -l /bin/sh /proc/boot/ksh /proc/boot/echo
lrwxrwxrwx 1 root root 14 Mar 20 07:52 /bin/sh -> /proc/boot/ksh
-r-xr-xr-x 1 root root 9390 Sep 12 2022 /proc/boot/echo
-r-xr-xr-x 1 root root 308114 Sep 12 2022 /proc/boot/ksh
```
