t: fix grep assertions missing file arguments

Three grep assertions were missing their file arguments, causing them to read from empty stdin instead of the intended file: - t2402: '! grep ...' should read from 'out', matching the grep on the preceding line. - t7507: the closing quote is in the wrong place, making the entire 'diff --git actual' a single pattern with no file argument instead of pattern 'diff --git' and file 'actual'. - t7700: '! grep ...' should read from 'packlist', matching the redirect on the preceding line. Without file arguments these greps always succeed (empty stdin matches nothing), so the assertions were not actually checking anything. All three tests pass with the corrected file arguments, confirming the intended behavior is sound. Signed-off-by: Michael Montalbo <mmontalbo@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>