Fix ocsp-stapling_tls13multi.test hang from unbounded server wait

Test cases 6 and 7 background the example server and then "wait" for it
to exit. When the server occasionally fails to exit (a timing race under
heavy parallel CI load), the script blocks until the job's
timeout-minutes, cancelling the whole trackmemory run - seen
consistently on the all-wolfentropy config.

Wrap those two servers in "timeout -s KILL 2m" (as scripts/dtls.test
already does) so a stuck server is killed and the test fails fast instead
of timing out the whole job.

scripts/ocsp-stapling_tls13multi.test

@@ -455,7 +455,7 @@ if [ "$tls13" == "yes" ]; then
 
     printf '%s\n\n' "------------- TEST CASE 6 LOAD CERT IN SSL -------------------"
     remove_single_rF "$ready_file5"
-    ./examples/server/server -c certs/ocsp/server1-cert.pem \
+    timeout -s KILL 2m ./examples/server/server -c certs/ocsp/server1-cert.pem \
                             -k certs/ocsp/server1-key.pem -R "$ready_file5" -v 4 \
                             -p "$port5" -H loadSSL &
     server_pid5=$!
@@ -470,7 +470,7 @@ if [ "$tls13" == "yes" ]; then
     printf '%s\n\n' "Test successful"
     printf '%s\n\n' "------------- TEST CASE 7 SHOULD REVOKE ----------------------"
     remove_single_rF "$ready_file5"
-    ./examples/server/server -c certs/ocsp/server4-cert.pem \
+    timeout -s KILL 2m ./examples/server/server -c certs/ocsp/server4-cert.pem \
                             -k certs/ocsp/server4-key.pem -R "$ready_file5" \
                             -p "$port5" -H loadSSL -v 4 &
     server_pid5=$!