tests: Add an address sanitizer suppression file

There are two places where we deliberately leak some memory. There are
some cases which look like leaks in libostree but it's not impossible
that we made a mistake in flatpak.

Two other cases seem like issues in flatpak that I couldn't figure out.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f