ztest: reduce runtile of zloop.sh in CI

The zloop.sh script is primarily designed to randomly stress
the DMU and SPA layers.  This can result in some unrealistic
(or even impossible) scenarios being tested which then fail.

Since the longer we run zloop.sh the more likely this is to occur
this commit reduces the runtime.  The intention being that normally
this will result in a clean CI run unless the PR does introduce
serious breaking change.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13453

.github/workflows/zloop.yml

@@ -38,8 +38,9 @@ jobs:
     - name: Tests
       run: |
         sudo mkdir -p $TEST_DIR
-        # run for 20 minutes to have a total runner time of 30 minutes
-        sudo /usr/share/zfs/zloop.sh -t 1200 -l -m1 -- -T 120 -P 60
+        # run for 10 minutes or at most 2 iterations for a maximum runner
+        #   time of 20 minutes.
+        sudo /usr/share/zfs/zloop.sh -t 600 -I 2 -l -m1 -- -T 120 -P 60
     - name: Prepare artifacts
       if: failure()
       run: |