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()'

[atulep]

This looks weird, but also potentially unsafe to remove.

[Axel-Jacobsen]

This is indeed weird, but is also safe.

Look at the last time it was changed (you will have to expand discover.py and scroll to line 701): 3bbefc1#diff-b039ba2bb64e79cf4c77e4fe5a4b21a826172e8b7ae9be872fd2d46047c05cbbL695-R701

Originally, it was

if type(value) == type("") or type(value) == type(u""):

But was changed automatically to be

if type(value) == type("") or type(value) == type(""):

because type("") == type(u"") == "str".

This if is redundant and pretty silly, and should be changed, no?