chore: improve assertion with expected path

[nbbeeken]

Description

What is changing?

Is there new documentation needed for these changes?

What is the motivation for this change?

A test failed and it isn't clear what part of the expectation wasn't an object.

https://spruce.mongodb.com/task/mongo_node_driver_next_rhel80_large_Node20_test_7.0_sharded_cluster_91d235221cc42a49bcfa85e428f83d8e6ba258d0_75c01e57abc470e785838d3c6dd0a8c0_25_03_18_15_22_09/logs?execution=0&sortBy=STATUS&sortDir=ASC

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[baileympearson]

assertion is much more actionable:

AssertionError: Expected actual ({ _id: 1, time: 2019-03-18T22:53:50.482Z }) to be an array at: events[2].commandStartedEvent.command.documents[0]: expected { _id: 1, time: 2019-03-18T22:53:50.482Z } to satisfy [Function]