Typing for optional function parameters are incorrect

[dcgudeman]

Environment details

• OS type and version: MacOS
• Python version: 3.11
• pip version: 23.3.1
• google-cloud-firestore version: 2.14.0

Steps to reproduce

1. Use a function that has an optional parameter
2. Observe type error

Code example

async_client = AsyncClient()
async_col_ref = async_client.collection("users")
all_users = async_col_ref.stream()

Stack trace

Argument of type "None" cannot be assigned to parameter "transaction" of type "Transaction" in function "stream"
  "None" is incompatible with "Transaction"Pylance[reportArgumentType](https://github.com/microsoft/pyright/blob/main/docs/configuration.md#reportArgumentType)

[daniel-sanche]

parent issue: #773

[daniel-sanche]

This should be fixed in #984