[stable15] Add test for updated CA bundle

[backportbot-nextcloud]

backport of #14373

[faily-bot]

🤖 beep boop beep 🤖

Here are the logs for the failed build:

Status of 16787: failure

DB=mysql, ENABLE_REDIS=false, PHP=7.3

Show full log

There was 1 failure:

1) TrashbinTest::testExpireOldFiles
Failed asserting that null is identical to 'file2.txt'.

/drone/src/github.com/nextcloud/server/apps/files_trashbin/tests/TrashbinTest.php:186

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There was 1 risky test:

1) OCA\TwoFactorBackupCodes\Tests\Db\BackupCodeMapperTest::testInsertArgonEncryptedCodes
This test did not perform any assertions

TESTS=acceptance, TESTS-ACCEPTANCE=app-files

• cancelled - typically means that the tests took longer than the drone CI allows them to run