Merge branch 'jk/ref-filter-trailer-fixes'

Merge branch 'jk/ref-filter-trailer-fixes'

Bugfixes and leak plugging in "git for-each-ref --format=..." code
paths.

* jk/ref-filter-trailer-fixes:
  ref-filter: fix leak with unterminated %(if) atoms
  ref-filter: add ref_format_clear() function
  ref-filter: fix leak when formatting %(push:remoteref)
  ref-filter: fix leak with %(describe) arguments
  ref-filter: fix leak of %(trailers) "argbuf"
  ref-filter: store ref_trailer_buf data per-atom
  ref-filter: drop useless cast in trailers_atom_parser()
  ref-filter: strip signature when parsing tag trailers
  ref-filter: avoid extra copies of payload/signature
  t6300: drop newline from wrapped test title