t5003: use binary file from t/lib-diff/

At some stage, t5003-archive-zip wants to add a file that is not ASCII.
To that end, it uses /bin/sh. But that file may actually not exist (it
is too easy to forget that not all the world is Unix/Linux...)! Besides,
we already have perfectly fine binary files intended for use solely by
the tests. So let's use one of them instead.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t5003-archive-zip.sh

@@ -88,7 +88,7 @@ test_expect_success \
     'mkdir a &&
      echo simple textfile >a/a &&
      mkdir a/bin &&
-     cp /bin/sh a/bin &&
+     cp "$TEST_DIRECTORY/lib-diff/test-binary-1.png" a/bin &&
      printf "text\r"	>a/text.cr &&
      printf "text\r\n"	>a/text.crlf &&
      printf "text\n"	>a/text.lf &&