bug#54608: 29.0.50; xref-search-program-alist: support ugrep

[Dmitry Gutov]

Hi Manuel,

On 31.03.2022 11:58, Manuel Uberti via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
> Hi Dmitry,
>
> is there something more you need me to do on this?

Both code and testing look good, thanks.

I've pushed the change in 9468ab2570.

Please take a look at the commit message, though. It would be helpful if 
your patches use the required format right away.