Suppress System.Threading.Lock cast to object errors

Author: stephentoub

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/Condition.cs

@@ -89,7 +89,9 @@ private unsafe void RemoveWaiter(Waiter waiter)
 
         public Condition(Lock @lock)
         {
+#pragma warning disable CS9216 // casting Lock to object
             ArgumentNullException.ThrowIfNull(@lock);
+#pragma warning restore CS9215
             _lock = @lock;
         }
 

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/SyncTable.cs

@@ -140,7 +140,7 @@ public static unsafe int AssignEntry(object obj, int* pHeader)
 
                     // Found a free entry to assign
                     Debug.Assert(!entry.Owner.IsAllocated);
-                    Debug.Assert(entry.Lock == null);
+                    Debug.Assert(entry.Lock is null);
                     Debug.Assert(entry.HashCode == 0);
 
                     // Set up the new entry.  We should not fail after this point.

src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/NativeRuntimeEventSource.Threading.NativeSinks.cs

@@ -5,6 +5,8 @@
 using System.Runtime.CompilerServices;
 using System.Threading;
 
+#pragma warning disable CS9216 // System.Threading.Lock cast to object for object identity
+
 namespace System.Diagnostics.Tracing
 {
     // This is part of the NativeRuntimeEventsource, which is the managed version of the Microsoft-Windows-DotNETRuntime provider.

src/libraries/System.Private.CoreLib/src/System/Threading/Lock.cs

@@ -130,7 +130,7 @@ internal Scope(Lock lockObj, ThreadId currentThreadId)
             public void Dispose()
             {
                 Lock? lockObj = _lockObj;
-                if (lockObj != null)
+                if (lockObj is not null)
                 {
                     _lockObj = null;
                     lockObj.Exit(_currentThreadId);