chg: usr: Reword the 'shut down hung fetch while resolving' message

The log message 'shut down hung fetch while resolving' may be confusing
because no detection of hung fetches actually takes place, but rather
the timer on the fetch context expires and the resolver gives up.

Change the log message to actually say that instead of the original
cryptic message about hung fetch.

Closes #3148

Merge branch '3148-rename-shut-down-hung-fetch' into 'main'

See merge request isc-projects/bind9!10759