Fix helix templates tests: strip class: prefix from test names

The send-to-helix-templatestests.targets was reading test class names from
.tests.list file which contains entries like "class:Aspire.Templates.Tests.ClassName".
It was using these entries directly without stripping the "class:" prefix,
causing issues in helix when the prefix was used as part of filenames or commands.

Now strips the "class:" prefix before using the test class names in helix work items.

Co-authored-by: radical <[email protected]>

Author: Copilot

tests/helix/send-to-helix-templatestests.targets

@@ -32,9 +32,14 @@
     </PropertyGroup>
 
     <ReadLinesFromFile File="$(TestArchiveTestsDirForTemplateTests)$(TestProjectName).tests.list">
-      <Output TaskParameter="Lines" ItemName="_TemplateTestsClassNames" />
+      <Output TaskParameter="Lines" ItemName="_TemplateTestsClassNamesRaw" />
     </ReadLinesFromFile>
 
+    <!-- Strip class: prefix from test class names -->
+    <ItemGroup>
+      <_TemplateTestsClassNames Include="@(_TemplateTestsClassNamesRaw->'%(Identity)'->Replace('class:', ''))" />
+    </ItemGroup>
+
     <Error Condition="@(_TemplateTestsClassNames->Count()) == 0"
            Text="No workload test class names found" />