[9.18] chg: doc: gitchangelog: don't break lines on hyphens in relnotes

When release notes are generated, the text is wrapped and line breaks
are inserted into each paragraph (sourced from the commit message's
body). Prevent line breaks after hyphens, as these are often used for
option names. This makes it possible to easily find the options
afterwards.

Backport of MR !9801

Merge branch 'backport-nicki/gitchangelog-dont-break-on-hyphens-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!9803