Bump Nullable from 1.3.0 to 1.3.1 (#626)

Bumps [Nullable](https://github.com/manuelroemer/Nullable) from 1.3.0 to 1.3.1.
- [Release notes](https://github.com/manuelroemer/Nullable/releases)
- [Changelog](https://github.com/manuelroemer/Nullable/blob/master/CHANGELOG.md)
- [Commits](https://github.com/manuelroemer/Nullable/commits)

---
updated-dependencies:
- dependency-name: Nullable
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

src/CodeGeneration/CodeGeneration.csproj

@@ -7,7 +7,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.3.1" />
     <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.3" PrivateAssets="all" />
-    <PackageReference Include="Nullable" Version="1.3.0">
+    <PackageReference Include="Nullable" Version="1.3.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>