Bump several dependencies

Author: AArnott

Directory.Packages.props

@@ -7,11 +7,11 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
-    <PackageVersion Include="xunit.runner.visualstudio" Version="2.8.1" />
-    <PackageVersion Include="xunit" Version="2.8.1" />
+    <PackageVersion Include="xunit.runner.visualstudio" Version="2.8.2" />
+    <PackageVersion Include="xunit" Version="2.9.0" />
   </ItemGroup>
   <ItemGroup>
-    <GlobalPackageReference Include="CSharpIsNullAnalyzer" Version="0.1.495" />
+    <GlobalPackageReference Include="CSharpIsNullAnalyzer" Version="0.1.593" />
     <GlobalPackageReference Include="DotNetAnalyzers.DocumentationAnalyzers" Version="1.0.0-beta.59" />
     <GlobalPackageReference Include="Nerdbank.GitVersioning" Version="3.6.139" />
     <GlobalPackageReference Include="Nullable" Version="1.3.1" />