Fix failing tests in TKTRawProcessHolderTest + Pharo 9

[tinchodias]

Tests: testStackContainsContextsOfMaster and testStackStartingAt.

After debugging a bit, I think it's the same root. A context is expected to head the stack but it isn't (identity equals is false). No idea.

[tinchodias]

In fact, these tests are part of TaskItDebugger, and it is broken since Pharo 9 since it depends on GTDebugger.
Time passed and I think we should remove this package from the default group, and open an issue to recover it.

[tinchodias]

Related issue: #109

[tinchodias]

In 6961207, I marked both tests as expected failures and I plan to let this issue open to remind they need attention.