tests: stablize test-serve.t on Windows

I forget the reason that the subprocess on Windows doesn't print this, but all
other instances of this are similarly conditionalized, so I didn't think too
hard about it.

Also, the server needs to be killed so it doesn't prevent the next run from
working, especially since the port isn't randomized.

Differential Revision: https://phab.mercurial-scm.org/D8720

tests/test-serve.t

@@ -103,7 +103,10 b' With out of bounds accesses'
 
 issue6362: Previously, this crashed on Python 3
 
-  $ hg serve -a 0.0.0.0 -d
-  listening at http://*:$HGPORT1/ (bound to *:$HGPORT1) (glob)
+  $ hg serve -a 0.0.0.0 -d --pid-file=hg.pid
+  listening at http://*:$HGPORT1/ (bound to *:$HGPORT1) (glob) (?)
+
+  $ cat hg.pid > "$DAEMON_PIDS"
+  $ "$PYTHON" $RUNTESTDIR/killdaemons.py $DAEMON_PIDS
 
   $ cd ..