roachtest: don't use smaller workload node for kv*/cpu=96 tests

Since the original change to use smaller workload nodes in kv tests, there have been several performance gains. As a result, the kv tests that use 96 cpu nodes are now being bottlenecked by the workload node.

This change now uses a larger workload node for those tests.

Release note: none
Fixes: none

2 files2 files	⊥	r1
Commits	⊥	r1
pkg/cmd/roachtest/tests/pkg/cmd/roachtest/tests/
kv.go	⊥	r1