Merge branch 'jk/for-each-ref-icase'

The "--ignore-case" option of "git for-each-ref" (and its friends) did not work correctly, which has been fixed. * jk/for-each-ref-icase: ref-filter: avoid backend filtering with --ignore-case for-each-ref: consistently pass WM_IGNORECASE flag t6300: add a test for --ignore-case