fix(parity): run peaceful_summon at midnight so zombie horses do not burn

Zombie horses are in the burn_in_daylight tag; Mob.isSunBurnTick rolls
every tick, so a horse could catch fire in the two-tick window and the
vanilla reference read 24 Health instead of 25 (#9089).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

tools/test_peaceful_summon_parity.py

@@ -68,6 +68,8 @@ def run_side(command, out, label):
         reply('tick freeze')
         reply('tick rate 200')
         assert any('false' in m for m in reply('gamerule minecraft:spawn_mobs false'))
+        # Zombie horses burn in daylight (Mob.isSunBurnTick rolls each tick), which made Health random.
+        reply('time set midnight')
         reply('forceload add 0 0 31 31')
         deadline = time.monotonic() + 300
         while True: