bug#56697: v. 3.7: Typo in man page

[Andrea Greselin]

Hi, there's a minor bug in grep's man page (at least in Fedora 36's version
of GNU grep 3.7). In the description of the flag '-P' there's written
    Interpret I<PATTERNS>  as…
with the markup instruction visible, instead of "PATTERNS" being in italics
or underlined.

Thanks for your work,
have a nice day,
Andrea