[Core] Update typing annotations for CaseInsensitive Dictionary (#25537)
[Core] Update typing annotations for CaseInsensitive Dictionary (#25537)

* update typing annotations

* change type

* typing fix

* fix type

* line too long pylint
Azure/azure-sdk-for-python,Azure/azure-sdk-for-python,Azure/azure-sdk-for-python,Azure/azure-sdk-for-python