tests: fix lingering wget in utils/trace.exp

It is apparently getting in the way of the rm test[1]:

    runner@fv-az1417-728:~/work/firejail/firejail/test/utils$
    <ail/test/utils$ firejail --trace wget -q debian.org
    5:wget:exec /usr/local/bin/wget:0
    5:wget:stat64 /etc/wgetrc:0
    5:wget:fopen64 /etc/wgetrc:0x561585600510
    5:wget:stat64 /home/runner/.wgetrc:-1
    OK
    [...]
    firejail --trace rm index.html
    5:wget:connect 4 128.31.0.62 port 443:0
    [...]
    5:wget:stat64 /home/runner/.wget-hsts:0
    runner@fv-az1417-728:~/work/firejail/firejail/test/utils$ TESTING ERROR 9

[1] https://github.com/kmk3/firejail/actions/runs/6004405511/job/16284920616

test/utils/trace.exp

@@ -80,6 +80,9 @@ expect {
 }
 sleep 1
 
+send -- "pkill wget\r"
+after 100
+
 send -- "firejail --trace rm index.html\r"
 expect {
 	timeout {puts "TESTING ERROR 9\n";exit}