build(deps): bump FodyHelpers from 6.6.4 to 6.7.0 in /src

Bumps [FodyHelpers](https://github.com/Fody/Fody) from 6.6.4 to 6.7.0.
- [Release notes](https://github.com/Fody/Fody/releases)
- [Commits](Fody/Fody@6.6.4...6.7.0)

---
updated-dependencies:
- dependency-name: FodyHelpers
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

src/ReactiveUI.Fody/ReactiveUI.Fody.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="MSBuild.Sdk.Extras">
+<Project Sdk="MSBuild.Sdk.Extras">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;net6.0;net7.0</TargetFrameworks>
     <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net472</TargetFrameworks>
@@ -8,6 +8,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="FodyHelpers" Version="6.6.4" />
+    <PackageReference Include="FodyHelpers" Version="6.7.0" />
   </ItemGroup>
 </Project>