Fix Site Isolation tests.
Fix Site Isolation tests.

The SingleProcessTracingBrowserTest.TestMemoryInfra is supposed to test
memory-infra for single process mode. So, running this test with
--site-per-process flag does not make sense. So, disabling the test for
this bot.

TBR=jam@chromium.org
BUG=462848

Review URL: https://codereview.chromium.org/1289983004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#343144}

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