Merge branch 'st/verify-tag'

Merge branch 'st/verify-tag'

"git tag" and "git verify-tag" learned to put GPG verification
status in their "--format=<placeholders>" output format.

* st/verify-tag:
  t/t7004-tag: Add --format specifier tests
  t/t7030-verify-tag: Add --format specifier tests
  builtin/tag: add --format argument for tag -v
  builtin/verify-tag: add --format to verify-tag
  ref-filter: add function to print single ref_array_item
  gpg-interface, tag: add GPG_VERIFY_OMIT_STATUS flag