move nlog back to AsyncLocal reentrancy check (#1830)

src/Sentry.NLog/SentryTarget.cs

@@ -265,7 +265,7 @@ protected override void FlushAsync(AsyncContinuation asyncContinuation)
             .FlushAsync(Options.FlushTimeout)
             .ContinueWith(t => asyncContinuation(t.Exception));
     }
-
+    static AsyncLocal<bool> isReentrant = new();
     /// <summary>
     /// <para>
     /// If the event level &gt;= the <see cref="MinimumEventLevel"/>, the
@@ -290,14 +290,13 @@ protected override void Write(LogEventInfo logEvent)
             return;
         }
 
-        const string sentryContext = "__sentry__";
-        if (GetContextNdlc(logEvent)?.Contains(sentryContext) is true)
+        if (isReentrant.Value)
         {
             Options.DiagnosticLogger?.LogError($"Reentrant log event detected. Logging when inside the scope of another log event can cause a StackOverflowException. LogEventInfo.Message:{logEvent.Message}");
             return;
         }
 
-        using var _ = NestedDiagnosticsLogicalContext.Push(sentryContext);
+        isReentrant.Value = true;
 
         try
         {
@@ -308,6 +307,10 @@ protected override void Write(LogEventInfo logEvent)
             Options.DiagnosticLogger?.LogError("Failed to write log event", exception);
             throw;
         }
+        finally
+        {
+            isReentrant.Value = false;
+        }
     }
 
     private void InnerWrite(LogEventInfo logEvent)