Update to Core 4.0

pyproject.toml

 [tool.poetry]
 name = "AlekSIS-App-DashboardFeeds"
-version = "3.0.1.dev0"
+version = "4.0.dev0"
 packages = [
     { include = "aleksis" }
 ]
@@ -44,7 +44,7 @@ python = "^3.9"
 feedparser = "^6.0.0"
 django-feed-reader = "^1.0.0"
 ics = "^0.7"
-aleksis-core = "^3.0"
+aleksis-core = "^4.0.0.dev0"
 
 [tool.poetry.plugins."aleksis.app"]
 dashboardfeeds = "aleksis.apps.dashboardfeeds.apps:DefaultConfig"