Unit test failures when running in parallel

[emteknetnz]

There are some unit test failures on framework when the unit tests are split up and run in parallel. This is possibly a result of bleed-over from tests leading to other tests passing. I'm not sure.

The issues are:

• Multiple instances of missing HierarchyTest* tables on MarkedSetTest and TreeMultiselectFieldTest
• SSViewerCacheBlockTest::testBlocksInvalidateOnFlush() having 1 vs 3 results return - it's a flush=1 is called and is testing filesystem caching

PRs

• MNT Fix unit tests when run in parallel #10724