binary diff: test that the diff and patch otputs are the same

We test the generation of the textual patch via the patch function,
which are just one of two possibilities to get the output.

Add a second patch generation via the diff function to make sure both
outputs are in sync.

tests/diff/binary.c

 #include "clar_libgit2.h"
 
+#include "git2/sys/diff.h"
+
 #include "buffer.h"
 #include "filebuf.h"
 
@@ -49,6 +51,11 @@ void test_patch(
 
 	cl_assert_equal_s(expected, actual.ptr);
 
+	git_buf_clear(&actual);
+	cl_git_pass(git_diff_print(diff, GIT_DIFF_FORMAT_PATCH, git_diff_print_callback__to_buf, &actual));
+
+	cl_assert_equal_s(expected, actual.ptr);
+
 	git_buf_free(&actual);
 	git_patch_free(patch);
 	git_diff_free(diff);