be more selective with appveyor build images

Author: bodewig

appveyor.yml

@@ -1,9 +1,8 @@
 version: 2.10.1.{build}
 
 image:
-  - Ubuntu2004
+  - Ubuntu2204
   - Visual Studio 2013
-  - Visual Studio 2017
   - Visual Studio 2022
 
 skip_tags: true
@@ -25,9 +24,8 @@ for:
 
   - matrix:
       only:
-        - image: Visual Studio 2017
         - image: Visual Studio 2022
-        - image: Ubuntu2004
+        - image: Ubuntu2204
     before_build:
       - dotnet restore XMLUnit.NET.sln
       - dotnet --version