Blender Git Loki

Guarded allocator: Fix lock-free allocator tests

Previously the lock-free tests were actually testing guarded allocator
because the main entry point of tests was switching allocator to the
guarded one.

There seems to be no allocations happening between the initialization
sequence and the fixture's SetUp(), so easiest seems to be just to
switch to lockfree implementation in the fixture's SetUp().

The test are passing locally, so the "should work" has high chance
of actually being truth :)

Differential Revision: https://developer.blender.org/D9584