Fix nullability error in portable thread pool (dotnet/coreclr#27366)

Commit migrated from https://github.com/dotnet/coreclr/commit/ddb1cf6abdc2ca54b1b6b5b4fa34bb2cdcbc9c3e

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/LowLevelLifoSemaphore.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/LowLevelLifoSemaphore.cs
index df5e234..a02dbd8 100644 (file)
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/LowLevelLifoSemaphore.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/LowLevelLifoSemaphore.cs
@@ -273,7 +273,7 @@ namespace System.Threading
 
             public static bool operator !=(Counts lhs, Counts rhs) => lhs._asLong != rhs._asLong;
 
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
             {
                 return obj is Counts counts && this._asLong == counts._asLong;
             }