chore: Move non-asserting boottime test to nightly CI

These tests are only there to collect metrics. With the boottime
A/B-test, we get that post-PR merge anyway, so only run these tests in
the nightly CI.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

tests/integration_tests/performance/test_boottime.py

@@ -165,6 +165,7 @@ def find_events(log_data):
     "vcpu_count,mem_size_mib",
     [(1, 128), (1, 1024), (2, 2048), (4, 4096)],
 )
+@pytest.mark.nonci
 def test_boottime(
     microvm_factory, guest_kernel, rootfs, vcpu_count, mem_size_mib, metrics
 ):