Add test for support Filter.With()

Turns out  support for `Filter.With(ILogEventFilter filter)` was already there since commit 4424523

Author: tsimbalar

test/Serilog.Settings.Configuration.Tests/ConfigurationSettingsTests.cs

@@ -991,5 +991,33 @@ public void EnrichWithIsAppliedWithCustomEnricher()
             Assert.NotNull(evt);
             Assert.True(evt.Properties.ContainsKey("ThreadId"), "Event should have enriched property ThreadId");
         }
+
+        [Fact]
+        public void FilterWithIsAppliedWithCustomFilter()
+        {
+            LogEvent evt = null;
+
+            var json = $@"{{
+                ""Serilog"": {{
+                    ""Using"": [""TestDummies""],
+                    ""Filter"": [
+                    {{
+                        ""Name"": ""With"",
+                        ""Args"": {{
+                            ""filter"": ""{typeof(DummyAnonymousUserFilter).AssemblyQualifiedName}""
+                        }}
+                    }}]
+                }}
+            }}";
+
+            var log = ConfigFromJson(json)
+                .WriteTo.Sink(new DelegatingSink(e => evt = e))
+                .CreateLogger();
+
+            log.ForContext("User", "anonymous").Write(Some.InformationEvent());
+            Assert.Null(evt);
+            log.ForContext("User", "the user").Write(Some.InformationEvent());
+            Assert.NotNull(evt);
+        }
     }
 }

test/TestDummies/DummyAnonymousUserFilter.cs

@@ -0,0 +1,25 @@
+
+using Serilog.Core;
+using Serilog.Events;
+
+namespace TestDummies
+{
+    public class DummyAnonymousUserFilter : ILogEventFilter
+    {
+        public bool IsEnabled(LogEvent logEvent)
+        {
+            if (logEvent.Properties.ContainsKey("User"))
+            {
+                if (logEvent.Properties["User"] is ScalarValue sv)
+                {
+                    if (sv.Value is string s && s == "anonymous")
+                    {
+                        return false;
+                    }
+                }
+            }
+
+            return true;
+        }
+    }
+}