fix: silence nontrivial memcall warning for clang >= 20

[supervacuus]

related parent PR: getsentry/sentry-native#1446

[supervacuus]

Uhm, just to be clear: this is a false positive. Yes, in theory this is only non-trivially copyable but those unions only contain POD. There is nothing inside that would bypass correct initialization with a memset. Ideally, upstream would do modern value initialization on one of the union tags in that ctor-list. But in the name of upstream maintainability I think disabling the false positive in the util build-script is the best choice.