ci: install .NET 10 SDK in UI tests build template

The .NET 10 upgrade (PR #41280) updated job-build-project.yml to install the
.NET 10 SDK on the agent, but missed the parallel change in job-build-ui-tests.yml,
which still pinned 'version: 9.0'.

As a result, the scheduled UI Test Automation pipeline (Dart/161438) has been
failing daily since 2026-04-30 with NETSDK1045 across all 179 csproj restores:

  error NETSDK1045: The current .NET SDK does not support targeting .NET 10.0.

Bump the pinned SDK version from 9.0 to 10.0 to match the rest of the pipeline.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: LegendaryBlair

.pipelines/v2/templates/job-build-ui-tests.yml

@@ -64,7 +64,7 @@ jobs:
   - template: steps-ensure-dotnet-version.yml
     parameters:
       sdk: true
-      version: '9.0'
+      version: '10.0'
 
   - template: .\steps-restore-nuget.yml