10.1.x compatibility: tests are failing against Drupal 10.1.x due to upstream changes

Problem/Motivation

Testing Drupal\Tests\cdn\Functional\CdnIntegrationTest
E.....F                                                             7 / 7 (100%)

Time: 00:33.242, Memory: 4.00 MB

There was 1 error:

1) Drupal\Tests\cdn\Functional\CdnIntegrationTest::testCss
Behat\Mink\Exception\ExpectationException: The string "url(" was not found anywhere in the HTML response of the current page.

/var/www/html/vendor/behat/mink/src/WebAssert.php:794
/var/www/html/vendor/behat/mink/src/WebAssert.php:324
/var/www/html/core/tests/Drupal/Tests/WebAssert.php:496
/var/www/html/modules/contrib/cdn/tests/src/Functional/CdnIntegrationTest.php:141
/var/www/html/modules/contrib/cdn/tests/src/Functional/CdnIntegrationTest.php:111
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestResult.php:728

--

There was 1 failure:

1) Drupal\Tests\cdn\Functional\CdnIntegrationTest::testFarfuture with data set "js" ('core/modules/system/js/system...les.js', ':relative:', 'core/modules/system/js/system...les.js', 'application/javascript')
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'application/javascript'
+'text/javascript; charset=UTF-8'

/var/www/html/vendor/phpunit/phpunit/src/Framework/Constraint/Constraint.php:122
/var/www/html/vendor/phpunit/phpunit/src/Framework/Constraint/IsIdentical.php:79
/var/www/html/modules/contrib/cdn/tests/src/Functional/CdnIntegrationTest.php:212
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestResult.php:728

The latter is caused by #84883: Unicode::mimeHeaderEncode() doesn't correctly follow RFC 2047 — see https://www.drupal.org/node/3312139

The former is I think caused by #1014086: Stampedes and cold cache performance issues with css/js aggregation — see https://www.drupal.org/node/2888767]

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes