test: skip tests related to CI failures on AIX

These tests seem to trigger failures in the entire CI job (not just the
test) on AIX. Skip them to see if that helps alleviate spurious failures
in node-test-commit-aix (and the upstream PR and commit test jobs).

See:
- https://github.com/nodejs/build/issues/1820#issuecomment-505998851
- https://github.com/nodejs/build/issues/1847#issuecomment-504210708

PR-URL: https://github.com/nodejs/node/pull/28469
Backport-PR-URL: https://github.com/nodejs/node/pull/28826


Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>