Fixup build warning (#39817)

Currently only appears only in VS

Fixes https://github.com/aspnet/AspNetCore-ManualTests/issues/1149

src/Components/Components/src/Sections/SectionRegistry.cs

@@ -88,7 +88,7 @@ internal sealed class SectionRegistry
         }
     }
 
-    private RenderFragment? GetCurrentProviderContentOrDefault(List<ISectionContentProvider> providers)
+    private static RenderFragment? GetCurrentProviderContentOrDefault(List<ISectionContentProvider> providers)
         => providers.Count != 0
             ? providers[^1].Content
             : null;