Use correct SVG icon on share view

[pixelipo]

Discovered while testing #7575 - it seems that $image-logo SCSS variable was pointing to a deprecated SVG image.
Before:

After:

[MorrisJobke]

Acceptance tests fail:

  Scenario: open the menu in a public shared link                   # /drone/src/github.com/nextcloud/server/tests/acceptance/features/app-files.feature:26
    Given I act as John                                             # ActorContext::iActAs()
    And I am logged in                                              # LoginPageContext::iAmLoggedIn()
    And I share the link for "welcome.txt"                          # FilesAppContext::iShareTheLinkFor()
    And I write down the shared link                                # FilesAppContext::iWriteDownTheSharedLink()
    When I act as Jane                                              # ActorContext::iActAs()
    And I visit the shared link I wrote down                        # FilesSharingAppContext::iVisitTheSharedLinkIWroteDown()
    And I see that the current page is the shared link I wrote down # FilesSharingAppContext::iSeeThatTheCurrentPageIsTheSharedLinkIWroteDown()
      Failed asserting that two strings are equal.
      --- Expected
      +++ Actual
      @@ @@
      -''
      +'about:blank'
    And I open the Share menu                                       # FilesSharingAppContext::iOpenTheShareMenu()
    Then I see that the Share menu is shown                         # FilesSharingAppContext::iSeeThatTheShareMenuIsShown()

[pixelipo]

That's baffling. This PR could not possibly cause that failure. Any ideas?

[juliusknorr]

The logo should not be stretched to the whole container when we use the default Nextcloud logo. Similar to #4910

[rullzer]

@pixelipo any chance you can take a look at the comment from @juliushaertl ?

[MorrisJobke]

Merged as #7670 🤣

[juliusknorr]

Addressed the logo sizing in #7678