Omit buffer test

[jmid]

The Buffer test can trigger a segfault as described in #63.
This KR therefore

• omits the test (temporarily) and
• wraps the domains functions in exception handlers (building on Wrap domain functions in a handler to ensure proper joining #69).

The hypothesis is that collectively the two will restore green CI lights for MacOS... 🤞

[jmid]

This is still failing with a segfault https://github.com/jmid/multicoretests/runs/6479465240?check_suite_focus=true#step:6:916

New hypothesis:

• this is caused by src/lazy_lin_test.ml
• it is tied to raising exceptions (here CamlinternalLazy.Undefined)
• it happens when finishing the test (completing the run of the first of 3 variants - so not at exit)

Still not reproducible locally - so trying to add missing handlers (while crossing fingers...)

[jmid]

Hypothesis shot down: last two MacOS CI runs resulted in 4 and 2 segfaults, respectively:

• https://github.com/jmid/multicoretests/runs/6483633874?check_suite_focus=true#step:6:501
• https://github.com/jmid/multicoretests/runs/6483633586?check_suite_focus=true#step:6:441

[jmid]

Closing as the MacOS CI is no longer segfaulting after switching to the alpha repo.