[OpenMP] Temporarily disable failing runtime tests for OpenMP 5.0

Following tests are failing after upgrading to version 5.0 but are passing
for version 4.5:
1. openmp/runtime/test/env/kmp_set_dispatch_buf.c
2. openmp/runtime/test/worksharing/for/kmp_set_dispatch_buf.c

To be enabled as soon as these tests are fixed.

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D82963