Describe the bug
Mongodb Atlas tests assume specific documents, collections and databases exists

so tests in test_embedding_retrieval automaticly fail

additionally test_embedding_retrieval and test_embedding_retrieval_async are searching for MONGO_CONNECTION_STRING_2 and till be skipped. I think this is a bug and we need to to replace MONGO_CONNECTION_STRING_2 with MONGO_CONNECTION_STRING

good news I am hard at working at a pr that will ensure this database, collection, documents will be created in an idempotent manner

To Reproduce
cd
git clone https://github.com/deepset-ai/haystack-core-integrations.git
cd haystack-core-integrations/integrations/mongodb_atlas
pip install hatch
export MONGO_CONNECTION_STRING = ""
hatch run test