update ms.topic to match new guidelines (#44707)

Author: gewarren

docfx.json

@@ -256,6 +256,7 @@
                 "docs/core/runtime-config/**.md": "reference",
                 "docs/core/tools/dotnet*.md": "reference",
                 "docs/core/tools/sdk-errors/*.md": "error-reference",
+                "docs/core/testing/mstest-analyzers/*.md": "error-reference",
                 "docs/core/tutorials/**.md": "tutorial",
                 "docs/csharp/getting-started/**/*.md": "overview",
                 "docs/csharp/how-to/**/*.md": "how-to",