Use new Lock class

Author: ejsmith

src/Foundatio.Mediator/HandlerGenerator.cs

@@ -538,7 +538,7 @@ private static void GenerateGetOrCreateHandler(IndentedStringBuilder source, Han
         source.AppendLine()
               .AppendLines($$"""
                 private static {{handler.FullName}}? _handler;
-                private static readonly object _lock = new object();
+                private static readonly global::System.Threading.Lock _lock = new();
 
                 [DebuggerStepThrough]
                 private static {{handler.FullName}} GetOrCreateHandler(IServiceProvider serviceProvider)

tests/Foundatio.Mediator.Tests/BasicHandlerGenerationTests.GeneratesWrapperForSimpleHandler.verified.txt

@@ -111,7 +111,7 @@ internal static class PingHandler_Ping_Handler
     }
 
     private static PingHandler? _handler;
-    private static readonly object _lock = new object();
+    private static readonly global::System.Threading.Lock _lock = new();
 
     [DebuggerStepThrough]
     private static PingHandler GetOrCreateHandler(IServiceProvider serviceProvider)
@@ -176,4 +176,4 @@ public static class Tests_MediatorHandlers
 
     }
   ]
-}
+}