ccanlint: don't collect results from test children

This confuses the output, and makes us sometimes see spurious
failure.  At least we will still catch valgrind errors in
children of failtest, thanks to --error-exitcode=101.

tools/ccanlint/tests/tests_pass_valgrind.c

@@ -112,6 +112,7 @@ static void do_run_tests_vg(struct manifest *m,
 			 * humans, and you can't have both. */
 			run_command(score, timeleft, &cmdout,
 				    "valgrind -q --error-exitcode=101"
+				    " --child-silent-after-fork=yes"
 				    " --leak-check=full"
 				    " --log-fd=3 %s %s"
 				    " 3> valgrind.log",