t: fix grep assertions missing file arguments

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 <redacted>
Signed-off-by: Junio C Hamano <redacted>