Undefined behavior from cereal/rapidjson in unit tests

[peddie]

The error is reported as:

/home/peddie/albatross/third_party/cereal/include/cereal/external/rapidjson/internal/stack.h:117:13: runtime error: applying non-zero offset 16 to null pointer

Here is a CI job that shows this error.

This issue has been fixed in upstream rapidjson in this commit about 2 years ago. Unfortunately cereal bundles its own version of rapidjson directly in the repo rather than relying on upstream or using a submodule, and what’s more, the bundled version appears to be customized for cereal, meaning it’s not a simple copy-and-paste PR to the cereal project.

[peddie]

I've suppressed this error in CI as part of #373.