[stable15] Have streams of files_external in sync

[rullzer]

Backport of #14579

[faily-bot]

🤖 beep boop beep 🤖

Here are the logs for the failed build:

Status of 16846: failure

TESTS=acceptance, TESTS-ACCEPTANCE=app-comments

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

TESTS=acceptance, TESTS-ACCEPTANCE=app-files

• tests/acceptance/features/app-files.feature:126

Show full log

  Scenario: show deleted files                                        # /drone/src/github.com/nextcloud/server/tests/acceptance/features/app-files.feature:126
    Given I am logged in                                              # LoginPageContext::iAmLoggedIn()
    And I delete "welcome.txt"                                        # FileListContext::iDelete()
    When I open the "Deleted files" section                           # AppNavigationContext::iOpenTheSection()
    Then I see that the current section is "Deleted files"            # AppNavigationContext::iSeeThatTheCurrentSectionIs()
    Then I see that the file list contains a file named "welcome.txt" # FileListContext::iSeeThatTheFileListContainsAFileNamed()
      Row for file welcome.txt in file list could not be found after 100 seconds (NoSuchElementException)

TESTS=acceptance, TESTS-ACCEPTANCE=app-files-sharing

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

TESTS=acceptance, TESTS-ACCEPTANCE=users

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