UT `conversions_suite/tiles_of_arrays_non_unit_blocking` times out w/ Pthreads and 2 ranks

[evaleev]

examples:

• https://github.com/ValeevGroup/tiledarray/actions/runs/6654216101/job/18081802650#step:8:3924
• https://github.com/ValeevGroup/tiledarray/actions/runs/6654216101/job/18081803248#step:8:4172
• https://github.com/ValeevGroup/tiledarray/actions/runs/6654216101/job/18081803787#step:8:3924

more facts:

• GitLab CI completed fine, so this seems to only happen w/ GitHub CI.
• All PaRSEC jobs completed.
• Not all Pthreads job time out: https://github.com/ValeevGroup/tiledarray/actions/runs/6654216101/job/18081802003#step:8:837

This is likely due to effects of oversubscription, as indicated by the greatly increased execution time of "nearby" UTs in the failing jobs compared to the successful jobs, e.g.compare

• failing: MacOS Release
• successful: Linux Release