Suppress expected errors in resource unit tests

[killzebug]

The test "[Resource] Breaking circular references on save" produces errors

ERROR: Resource was not pre cached for the resource section, bug?
   at: _write_resource (scene/resources/resource_format_text.cpp:1882)
WARNING: Couldn't load resource (no cache): local://Resource_agy4p
     at: parse_variant (core/io/resource_format_binary.cpp:412)

The errors are intentional because the test uses uncached internal resources and as a result of the test the circular reference is broken. I tested out the branchpath in ResourceFormatSaverBinaryInstance::_find_resources that mentions circular references and found that it skips over internal resources.
I have only suppressed the parts that produce errors: saving to text and loading from binary.
Fixes: #80616

[akien-mga]

Thanks for the contribution! This seems sensible to me.

Could you amend the commit message to be more explicit? E.g. like you used for the PR itself.

[killzebug]

Changed the comment, should be good to go.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉