Reduce timeout when waiting for PRs

The previous value of 7200 minutes equals 5 days, which is far too long.
Reduce it to 4 hours, which brings the latest start time for the AliPhysics
builds down to 19:00 UTC (20:00 CET / 21:00 CEST). This should still be long
enough to wait for any remaining PRs to finish testing and be merged.

jenkins/daily-tags

@@ -15,7 +15,7 @@ try {
   stage "Wait pull requests"
   if ("$WAIT_PR" == "true") {
     node ("slc7_x86-64-light") {
-      timeout (7200) {
+      timeout (240) {
         withEnv(["ALIBOT_SLUG=${ALIBOT_SLUG}",
                  "WAIT_PR_LIMIT=${WAIT_PR_LIMIT}",
                  "PACKAGES=${PACKAGES}"]) {