Scope NU5052 warning to SDK projects only

Only emit the restricted package ID warning (NU5052) when
UsingMicrosoftNETSdk is true. Non-SDK projects (nuget.exe pack)
do not emit this warning.

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

Author: nkolev92

src/NuGet.Core/NuGet.Commands/CommandRunners/PackCommandRunner.cs

@@ -117,7 +117,7 @@ private bool BuildPackage(PackageBuilder builder, string outputPath = null, bool
             Directory.CreateDirectory(Path.GetDirectoryName(outputPath));
 
             // Warn if the package ID doesn't adhere to the restricted character set (NU5052)
-            if (!symbolsPackage && !PackageIdValidator.IsValidPackageId(builder.Id, useRestrictedCharacterSet: true))
+            if (!symbolsPackage && _packArgs.UsingMicrosoftNETSdk && !PackageIdValidator.IsValidPackageId(builder.Id, useRestrictedCharacterSet: true))
             {
                 if (SdkAnalysisLevelMinimums.IsEnabled(_packArgs.SdkAnalysisLevel, _packArgs.UsingMicrosoftNETSdk, SdkAnalysisLevelMinimums.V11_0_100))
                 {

test/NuGet.Core.Tests/NuGet.Commands.Test/PackCommandRunnerTests.cs

@@ -264,7 +264,7 @@ public void Dispose()
         [InlineData("Contöso.Utilities", "11.0.100", true, true)]       // non-ASCII ö, enabled → emits
         [InlineData("\u0421ontoso.Utilities", "11.0.100", true, true)]   // Cyrillic С, enabled → emits
         [InlineData("Contöso.Utilities", "10.0.100", true, false)]      // below threshold → suppressed
-        [InlineData("Contöso.Utilities", null, false, true)]            // non-SDK project (nuget.exe) → emits
+        [InlineData("Contöso.Utilities", null, false, false)]            // non-SDK project (nuget.exe) → not emitted (SDK-only warning)
         [InlineData("Contöso.Utilities", null, true, false)]            // SDK project, no level (assumes 8.0.400) → suppressed
         public void BuildPackage_PackageIdWithInvalidCharacters_EmitsNU5052_BasedOnSdkAnalysisLevel(string packageId, string? sdkAnalysisLevel, bool usingMicrosoftNETSdk, bool expectWarning)
         {