Use Botan 3.1.1 for tests

Use Botan 3.1.1 for tests

The all-zero Ed25519 public key is rejected by botan_pubkey_check_key()
when the key is loaded.

Note that Botan 3 requires GCC 11 or CLANG 14, i.e. can't easily be built
on Debian bullseye or Ubuntu 20.04.

The thread-local storage function gets flagged via various botan FFI
functions when using Botan 3, whitelist that instead of all of them.