java/time/format/TestZoneTextPrinterParser.java test frequently times out in aggressive GC tests. For example, Shenandoah tests that run a lot of verification on every cycle take a lot of time. Ultimately, this seems to be because the test runs in too tight heap, so GCs are very frequent. Increasing the heap size makes the test run faster:

# -XX:+UseShenandoahGC -XX:ParallelGCThreads=1 -XX:+ShenandoahVerify -Xmx512m (default)
[> 30 minutes, timeout]

# -XX:+UseShenandoahGC -XX:ParallelGCThreads=1 -XX:+ShenandoahVerify -Xmx768m
real 7m8.854s
user 10m55.716s
sys 0m7.472s

# -XX:+UseShenandoahGC -XX:ParallelGCThreads=1 -XX:+ShenandoahVerify -Xmx1g
real 6m7.767s
user 10m11.455s
sys 0m7.725s

# -XX:+UseShenandoahGC -XX:ParallelGCThreads=1 -XX:+ShenandoahVerify -Xmx2g
real 3m42.963s
user 7m19.833s
sys 0m8.849s

# -XX:+UseShenandoahGC -XX:ParallelGCThreads=1 -XX:+ShenandoahVerify -Xmx4g
real 3m0.635s
user 6m20.024s
sys 0m9.158s

# -XX:+UseShenandoahGC -XX:ParallelGCThreads=1 -XX:+ShenandoahVerify -Xmx8g
real 2m6.565s
user 5m20.167s
sys 0m10.450s

I think we can settle on -Xmx2g here.