build(deps): bump Avalonia from 0.10.12 to 0.10.18 in /src

Bumps [Avalonia](https://github.com/AvaloniaUI/Avalonia) from 0.10.12 to 0.10.18.
- [Release notes](https://github.com/AvaloniaUI/Avalonia/releases)
- [Commits](AvaloniaUI/Avalonia@0.10.12...0.10.18)

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

Signed-off-by: dependabot[bot] <[email protected]>

src/Sextant.Avalonia/Sextant.Avalonia.csproj

@@ -9,7 +9,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="ReactiveUI" Version="17.*" />
-    <PackageReference Include="Avalonia" Version="0.10.12" />
+    <PackageReference Include="Avalonia" Version="0.10.18" />
     <PackageReference Include="Avalonia.Desktop" Version="0.10.12" />
     <PackageReference Include="Avalonia.ReactiveUI" Version="0.10.12" />
   </ItemGroup>