chore(deps): update dependency system.reactive to v7 (#460)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

src/Directory.Packages.props

@@ -31,7 +31,7 @@
     <PackageVersion Include="Splat" Version="20.0.0" />
     <PackageVersion Include="ReactiveUI" Version="23.2.28" />
     <PackageVersion Include="ReactiveUI.Maui" Version="23.2.28" />
-    <PackageVersion Include="System.Reactive" Version="6.1.0" />
+    <PackageVersion Include="System.Reactive" Version="7.0.0" />
     <PackageVersion Include="TUnit" Version="1.61.15" />
     <PackageVersion Include="Verify.TUnit" Version="31.20.0" />
     <PackageVersion Include="Verify.SourceGenerators" Version="2.5.0" />