chore: use isinstance() instead of type comparison

[parthea]

Fixes warning from flake8 . --select E721

(py39) partheniou@partheniou-vm-2:~/git/google-api-python-client$ flake8 . --select E721
./googleapiclient/model.py:177:28: E721 do not compare types, use 'isinstance()'
./googleapiclient/model.py:396:37: E721 do not compare types, use 'isinstance()'
./googleapiclient/discovery.py:701:24: E721 do not compare types, use 'isinstance()'
./googleapiclient/discovery.py:712:24: E721 do not compare types, use 'isinstance()'
./googleapiclient/discovery.py:1078:66: E721 do not compare types, use 'isinstance()'