Remove the space before the interpreter name in test-network.sh

Apparently some unixes don't like this.
Part of #21581.

src/test/test-network.sh

@@ -1,4 +1,4 @@
-#! /bin/sh
+#!/bin/sh
 
 # use bash if it is available, as this script doesn't work well in non-bash sh
 # this will be fixed in #19699