Merge branch 'hv/ref-filter-trailers-atom-parsing-fix'

The parser for "git for-each-ref --format=..." was too loose when parsing the "%(trailers...)" atom, and forgot that "trailers" and "trailers:<modifiers>" are the only two allowed forms, which has been corrected. * hv/ref-filter-trailers-atom-parsing-fix: ref-filter: 'contents:trailers' show error if `:` is missing t6300: unify %(trailers) and %(contents:trailers) tests