npcm7xx_timer-test.c is unreliable

Description of problem

Sometimes npcm7xx_timer-test fails intermittently: https://gitlab.com/qemu-project/qemu/-/jobs/5121787250

38/96 qemu:qtest+qtest-arm / qtest-arm/npcm7xx_timer-test           ERROR           0.95s   exit status 1
>>> QTEST_QEMU_BINARY=./qemu-system-arm QTEST_QEMU_STORAGE_DAEMON_BINARY=./storage-daemon/qemu-storage-daemon G_TEST_DBUS_DAEMON=/builds/qemu-project/qemu/tests/dbus-vmstate-daemon.sh QTEST_QEMU_IMG=./qemu-img MALLOC_PERTURB_=103 /builds/qemu-project/qemu/build/tests/qtest/npcm7xx_timer-test --tap -k
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stderr:
**
ERROR:../tests/qtest/npcm7xx_timer-test.c:475:test_periodic_interrupt: assertion failed (tim_read(td, TISR) == tim_timer_bit(td)): (0x00000000 == 0x00000004)
**
ERROR:../tests/qtest/npcm7xx_timer-test.c:476:test_periodic_interrupt: 'qtest_get_irq(global_qtest, tim_timer_irq(td))' should be TRUE
(test program exited with status code 1)
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When I reran the CI job, it passed.

Please investigate why this test is unreliable and fix it. Thanks!