tests: arrange for a server in wireproto-command-capabilities.t to be killed

The stray servers were piling up after the test harness exited.  On Windows,
this means the *.pyd files can't be rebuilt, which is why the build warning
count dropped to 1 recently.

tests/test-wireproto-command-capabilities.t

@@ -142,6 +142,7 b' Restart server to enable HTTPv2'
   $ killdaemons.py
   $ enablehttpv2 server
   $ hg -R server serve -p $HGPORT -d --pid-file hg.pid -E error.log
+  $ cat hg.pid > $DAEMON_PIDS
 
 Only requested API services are returned