Update to dotnet 8 preview 5 (#14492)

* Update to .net 8 preview 1

* Update npoco to 5.7.0

* Update pipeline to use .net 8

* Revert "Update npoco to 5.7.0"

This reverts commit f7795afa77a41ef2719f639405f73d9c21e4b12e.

* Fix tests and updated OpenApi.json

* use dotnet 8 in linux container

* Updated templates and docker image to dotnet 8

* Bugfix

* R
Updated docker images to 8.0 preview 1

* linux docker images updated

* Force use c# 11, in hope of the acceptance tests will pass

* Do not use C# 8 :)

* Update to preview 2

* CompatibilitySuppressions

* updated templates

* Disable package validation

* Update to .net8 preview 4

* change EnableStrictModeForCompatibleFrameworksInPackage to false

* Package validation

* Added CompatibilitySuppressions.xml

* Fix up IP networks

* Updated to preview 5

* Update docker images

* Post merge fixes

* Try to update dotnet version of codeql

* Delete empty suppression files

* Remove dependency

* Cleanup

---------

Co-authored-by: Elitsa <elm@umbraco.dk>

src/Umbraco.Web.BackOffice/Umbraco.Web.BackOffice.csproj

@@ -7,10 +7,6 @@
     <RootNamespace>Umbraco.Cms.Web.BackOffice</RootNamespace>
   </PropertyGroup>
 
-  <ItemGroup>
-    <FrameworkReference Include="Microsoft.AspNetCore.App" />
-  </ItemGroup>
-
   <ItemGroup>
     <PackageReference Include="Markdown" Version="2.2.1" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
@@ -33,4 +29,4 @@
   <ItemGroup>
     <EmbeddedResource Include="EmbeddedResources\**\*" />
   </ItemGroup>
-</Project>
+</Project>