Bump System.Memory and System.Text.Encoding.CodePages

Bumps System.Memory and [System.Text.Encoding.CodePages](https://github.com/dotnet/runtime). These dependencies needed to be updated together.

Updates `System.Memory` from 4.5.5 to 4.5.5

Updates `System.Text.Encoding.CodePages` from 8.0.0 to 9.0.0
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v8.0.0...v9.0.0)

---
updated-dependencies:
- dependency-name: System.Memory
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: System.Text.Encoding.CodePages
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

src/Slugify.Core/Slugify.Core.csproj

@@ -53,7 +53,7 @@ With default settings, you will get an hyphenized, lowercase, alphanumeric versi
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="System.Memory" Version="4.5.5" />
-    <PackageReference Include="System.Text.Encoding.CodePages" Version="8.0.0" />
+    <PackageReference Include="System.Text.Encoding.CodePages" Version="9.0.0" />
   </ItemGroup>