Bump sabre/dav to 4.1

[ChristophWurst]

Same same as #492 but with composer v1.

[juliusknorr]

Check is not happy:

Uncommited vendor changes
HEAD detached at pull/551/merge
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   composer/ClassLoader.php
	modified:   composer/InstalledVersions.php
	modified:   composer/autoload_classmap.php
	modified:   composer/autoload_real.php
	modified:   composer/autoload_static.php
	modified:   composer/installed.json
	modified:   composer/installed.php

[ChristophWurst]

Check is not happy:

Yeah, because the check uses composer v2. Recently we never had green CI here. If you can satisfy it thou please feel free to push another commit to my branch :)