Update testserver.py reverting upstream change

[andreagalle]

The .self.path.endswith( are necessary, as well as the "cross-origin-embedder-policy", "unsafe-none" header.

• Which sense this header is buggy, as the comment states?
• Does it make sense to apply the same patch ( .self.path.endswith( ) even to the lines here below?

107        if path.endswith("/"):

...

114        invalid = path.endswith(".map") or path.endswith(".apk")