Fix warnings

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockDirectoryTests.cs

@@ -2113,7 +2113,7 @@ public async Task MockDirectory_SetCreationTime_ShouldNotThrowWithoutTrailingBac
             var path = XFS.Path(@"C:\NoTrailingBackslash");
             var fs = new MockFileSystem();
             fs.Directory.CreateDirectory(path);
-            fs.Directory.SetCreationTime(path, DateTime.Now);
+            await That(()=> fs.Directory.SetCreationTime(path, DateTime.Now)).DoesNotThrow();
             fs.Directory.Delete(path);
         }
 

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileTests.cs

@@ -492,7 +492,7 @@ public async Task MockFile_Delete_No_File_Does_Nothing()
 
             string filePath = XFS.Path(@"c:\something\not_exist.txt");
 
-            fileSystem.File.Delete(filePath);
+            await That(() => fileSystem.File.Delete(filePath)).DoesNotThrow();
         }
 
         [Test]
@@ -550,7 +550,7 @@ public async Task MockFile_AppendText_CreatesNewFileForAppendToNonExistingFile()
 
 #if !NET9_0_OR_GREATER
         [Test]
-        public async Task Serializable_works()
+        public void Serializable_works()
         {
             //Arrange
             MockFileData data = new MockFileData("Text Contents");