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")

[pmp-p]

for things that are clear to me:

• testing path is faster because it's a local
• path does not have ? # trail so it works with endswith() unlike self.path which is full url from http request

for those which are not:

The comment is a silly remnant of some blind experimentation.
But it could be changed to without "require-corp" or "credentialless" Atomics/threads/SharedArraybufers won't work.

https://partytown.builder.io/tests/atomics/?coep=require-corp <= seems the one that work better than credentialless and is found on the targeted hosting websites.

Note that the runtime still don't use those fancy features but it may require them in the future so better be ready for them.