Fix TUnit filter argument forwarding (#597)

Pass the tree-node filter as a single option argument for managed and NativeAOT test runs to avoid platform-specific argument parsing failures.

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

Author: AArnott

tools/dotnet-test-cloud.ps1

@@ -75,8 +75,7 @@ if ($isMTP) {
         ,'--crash-report-if-supported'
     )
     $mtpArgs = @(
-        ,'--treenode-filter'
-        ,'/*/*/*/*[TestCategory!=FailsInCloudTest]'
+        ,'--treenode-filter=/*/*/*/*[TestCategory!=FailsInCloudTest]'
         ,'--diagnostic'
         ,'--diagnostic-output-directory',$testLogs
         ,'--diagnostic-verbosity','Information'
@@ -119,8 +118,7 @@ if ($isMTP) {
             }
 
             $nativeAotArgs = @(
-                ,'--treenode-filter'
-                ,'/*/*/*/*[TestCategory!=FailsInCloudTest]'
+                ,'--treenode-filter=/*/*/*/*[TestCategory!=FailsInCloudTest]'
                 ,'--diagnostic'
                 ,'--diagnostic-output-directory',$testLogs
                 ,'--diagnostic-verbosity','Information'