Disable desktop CLR and single-file DAC tests blocked by CDB SecureLoadDotNetExtensions (#5759)

## Summary

Contributes to #5757

CDB 10.0.26100.1 introduced `SecureLoadDotNetExtensions` which verifies
digital signatures of DAC DLLs before loading them. Both the .NET
Framework `mscordacwks.dll` (from local Framework directory and symbol
server) and servicing .NET Core DAC DLLs fail this verification, causing
16 test failures across all Windows legs:

```
Failed to verify signature of file: C:\Windows\Microsoft.Net\Framework64\v4.0.30319\mscordacwks.dll
Error code - 0x000021BE
Debugger.Settings.EngineInitialization.SecureLoadDotNetExtensions is enabled, set to false to disable.
Failed to load data access module, 0x80004002
```

## Root Cause

The test infrastructure conditionally enables
`SecureLoadDotNetExtensions=true` for non-nightly, non-private builds.
CDB then rejects the DAC DLLs because their signatures cannot be
verified:
- `.NET Framework DAC` — `mscordacwks.dll` from
`C:\Windows\Microsoft.Net\Framework64\v4.0.30319\` and from the symbol
server
- `Servicing .NET Core DAC` — for .NET 8.0 servicing runtimes

This affects three test categories:
- **13 `desktop.cli` tests** — desktop CLR DAC signature verification
fails
- **2 `projectk.sdk.prebuilt` tests** (DualRuntimes) — desktop CLR
portion of dual-runtime dump fails
- **1 `projectk.cli.singlefile` test** (StackAndOtherTests) — .NET 8.0
servicing DAC fails

## Changes

All changes are in `SOS.cs` — disable the affected tests until the CDB
signing issue is resolved:

1. **Exclude desktop CLR configurations** from `SOS.Configurations` —
filters out `IsDesktop` configs that rely on `mscordacwks.dll`
2. **Skip `StackAndOtherTests`** for single-file on Windows — .NET 8.0
servicing DAC signature verification fails under CDB
3. **Skip `DualRuntimes`** on Windows — desktop CLR DAC portion of
dual-runtime dump fails

## Impact

- Disables **16 tests** blocked by CDB DAC signature verification
failures
- Tests can be re-enabled once the signing issue with the CDB package is
resolved (tracked by #5757)
- Test-only change — no product code or test infrastructure changes

---------

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

Author: steveisok

src/tests/SOS.UnitTests/SOS.cs

@@ -251,7 +251,11 @@ public SOS(ITestOutputHelper output)
 
     private ITestOutputHelper Output { get; set; }
 
-    public static IEnumerable<object[]> Configurations => SOSTestHelpers.GetConfigurations("TestName", value: null);
+    // Desktop CLR configurations are temporarily excluded because CDB SecureLoadDotNetExtensions
+    // and dotnet-dump DacSignatureVerification reject desktop CLR DAC DLLs.
+    // Tracking: https://github.com/dotnet/diagnostics/issues/5757
+    public static IEnumerable<object[]> Configurations => SOSTestHelpers.GetConfigurations("TestName", value: null)
+        .Where(args => !((TestConfiguration)args[0]).IsDesktop);
 
     [SkippableTheory, MemberData(nameof(SOSTestHelpers.GetNetCoreConfigurations), MemberType = typeof(SOSTestHelpers))]
     public async Task MiniDumpLocalVarLookup(TestConfiguration config)
@@ -546,6 +550,12 @@ await SOSTestHelpers.RunTest(
     [SkippableTheory, MemberData(nameof(SOSTestHelpers.GetConfigurations), "TestName", "SOS.StackAndOtherTests", MemberType = typeof(SOSTestHelpers))]
     public async Task StackAndOtherTests(TestConfiguration config)
     {
+        // Single-file .NET 8 servicing DAC signature verification fails with CDB SecureLoadDotNetExtensions.
+        // Tracking: https://github.com/dotnet/diagnostics/issues/5757
+        if (OS.Kind == OSKind.Windows && config.PublishSingleFile)
+        {
+            throw new SkipTestException("Single-file DAC signature verification failure with CDB (https://github.com/dotnet/diagnostics/issues/5757)");
+        }
         if (config.RuntimeFrameworkVersionMajor == 10)
         {
             // The clrstack -i -a command regressed on .NET 10 win-x86, so skip this test for now.
@@ -624,6 +634,13 @@ public async Task DualRuntimes(TestConfiguration config)
         {
             throw new SkipTestException("Single file not supported");
         }
+        // Desktop CLR DAC signature verification fails with CDB SecureLoadDotNetExtensions
+        // and dotnet-dump DacSignatureVerification.
+        // Tracking: https://github.com/dotnet/diagnostics/issues/5757
+        if (OS.Kind == OSKind.Windows)
+        {
+            throw new SkipTestException("Desktop CLR DAC signature verification failure (https://github.com/dotnet/diagnostics/issues/5757)");
+        }
         // The assembly path, class and function name of the desktop test code to load/run
         string desktopTestParameters = TestConfiguration.MakeCanonicalPath(config.GetValue("DesktopTestParameters"));
         if (string.IsNullOrEmpty(desktopTestParameters))