mongodb[patch]: Set delete_many only if count_documents is not 0 (#18402)

- [x] **PR message**: ***Delete this entire checklist*** and replace
with
- **Description:** Remove the assert statement on the `count_documents`
in setup_class. It should just delete if there are documents present
    - **Issue:** the issue # Crashes on class setup
    - **Dependencies:** None
    - **Twitter handle:** @mongodb


- [x] **Add tests and docs**: If you're adding a new integration, please
include
  1. N/A


- [ ] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
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If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, hwchase17.

Co-authored-by: Jib <jib@byblack.us>

libs/partners/mongodb/tests/integration_tests/test_vectorstores.py

@@ -50,7 +50,8 @@ class TestMongoDBAtlasVectorSearch:
     def setup_class(cls) -> None:
         # insure the test collection is empty
         collection = get_collection()
-        assert collection.count_documents({}) == 0  # type: ignore[index]  # noqa: E501
+        if collection.count_documents({}):
+            collection.delete_many({})  # type: ignore[index]  # noqa: E501
 
     @classmethod
     def teardown_class(cls) -> None: