timeout.test: fix test for systems that don't have bash.

(Such as Android.)

tests/timeout.test

@@ -22,7 +22,7 @@ testcmd "--preserve-status killed" '--preserve-status -s 9 .1 sleep 100 ; echo $
 # There's another special case where if the subprocess catches our timeout
 # signal and exits, we need to report that as a timeout (unless overridden).
 cat > loop.sh <<EOF
-#!/bin/bash
+#!/bin/sh
 trap "exit 3" SIGTERM
 while true; do
   :