[stable19] Better error message when blocked by access control

[backportbot-nextcloud]

backport of #22577

[faily-bot]

🤖 beep boop beep 🤖

Here are the logs for the failed build:

Status of 32653: failure

mysql8.0-php7.2

Show full log

There were 2 warnings:

1) Test\Files\ViewTest::testRenameFailDeleteTargetKeepSource
Trying to configure method "writeStream" which cannot be configured because it does not exist, has not been specified, is final, or is static

2) Test\Files\ViewTest::testCopyFailDeleteTargetKeepSource
Trying to configure method "writeStream" which cannot be configured because it does not exist, has not been specified, is final, or is static

--

There was 1 failure:

1) Test\Files\Config\UserMountCacheTest::testChangeMountId
Failed asserting that actual size 0 matches expected size 1.

/drone/src/tests/lib/Files/Config/UserMountCacheTest.php:210