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