Enable `sem.malloc.fail` or set `sem.malloc.zero` to `pointer` for SV-COMP 2027

[sim642]

Based on my observation in PR #1885, we lost a few tasks with PR #1777 not being configured for SV-COMP 2026. For SV-COMP 2027 one of the following should happen:

1. If rules are changed to allow malloc to fail, then our svcomp conf for 2027 should enable sem.malloc.fail.
2. Otherwise, it should set sem.malloc.zero to pointer to get back a few tasks.

Which of the two will actually happen will become apparent sometime during the next year.