If the filelib tests get a response via http2 instead of http, the core filelib test fails as the response returned is slightly different.

1) core\filelib_test::test_curl_useragent

Failed asserting that two strings are identical.

— Expected

+++ Actual

@@ @@

-'200 OK'

+'200 '

You can reproduce this via curl by forcing a specific http protocol

Default: (http2)

$ curl -I https://download.moodle.org/unittest/test.html

HTTP/2 200 

date: Mon, 21 Aug 2023 23:26:38 GMT

http1.1

 curl --http1.1 -I https://download.moodle.org/unittest/test.html

HTTP/1.1 200 OK

Date: Mon, 21 Aug 2023 23:27:08 GMT 

I'm not sure if this is related to cloudflare swapping a preferred default or a curl behaviour change that has finally filtered into the LMS.

As a workaround you can host your own version of the external test web docker and make sure it only returns http1.1 protocol responses.