[http-client-python] Align param type in description

[YalinLi0312]

Got a comment from a tsp migration PR: Azure/azure-sdk-for-python#37438 (comment)

This is the description of param credential in auto generated async client:

Expected:
It should be AsyncTokenCredential in param description as well.

[iscai-msft]

@YalinLi0312 we like our type descriptions to remain sync / async neutral, so it's kind of a difficult change actually to have it show up as async token credential in our documentation. How would you feel about "token credential type" instead of "TokenCredential type", so it's not directly associated with the TokenCredential object. "Token credential" as a concept is sansio