`external-http` test failures in 4.1-4.5 branches

[desrosj]

A new test failure has started occurring in the 4.5 branch and earlier.

1) Tests_HTTP_streams::test_ssl
stream_socket_client(): SSL operation failed with code 1. OpenSSL Error messages:
error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed

/var/www/src/wp-includes/class-wp-http-streams.php:150
/var/www/src/wp-includes/class-http.php:433
/var/www/src/wp-includes/class-http.php:342
/var/www/src/wp-includes/class-http.php:496
/var/www/src/wp-includes/http.php:170
/var/www/tests/phpunit/tests/http/base.php:387

On December 2, w.org switched to using Lets Encrpyt, which seems to be causing the problem.

[desrosj]

I'm not quite sure exactly why the failure is occurring yet, but applying [48707] to the branches fixes the problem.

It's also possibly related to ​https://letsencrypt.org/2024/03/19/new-intermediate-certificates/.

Trac ticket: https://core.trac.wordpress.org/ticket/62711