Here's a shell session illustrating the problem on Fedora 37, which has
GNU grep 3.7. The same bug is still in bleeding-edge GNU grep.
$ export LC_ALL=en_US.utf8
$ printf '\300\n' | grep '\b'
grep: (standard input): binary file matches
$ printf '\300\n' | grep -P '\b'
$
Plain grep finds a word boundary in the input even though the input
contains no words (just an encoding error). 'grep -P' does the right thing.
The underlying issue is in the glibc regex code so the fix should be in
glibc / Gnulib, but I thought I'd report it here before I forgot it.
