Fix flaky ClaimTypesConst tests

Tests/RCommon.Security.Tests/AssemblyInfo.cs

@@ -0,0 +1,10 @@
+using Xunit;
+
+// Several test classes in this assembly exercise ClaimTypesConst, which is a process-wide mutable
+// static (configure-once-at-startup). ClaimTypesConstTests and ClaimsIdentityExtensionsTests both
+// call the internal ClaimTypesConst.Reset() in their constructor/Dispose for isolation. Under xUnit's
+// default per-class parallelism these classes race on that global: a parallel Reset() can null the
+// options mid-test, so a subsequent property read rebuilds defaults and a configured value (e.g. a
+// custom Role) reverts to the default claim URI. Serialize the assembly's tests to make the shared
+// static state deterministic.
+[assembly: CollectionBehavior(DisableTestParallelization = true)]