Bump System.Memory from 4.5.5 to 4.6.0

Bumps [System.Memory](https://github.com/dotnet/maintenance-packages) from 4.5.5 to 4.6.0.
- [Release notes](https://github.com/dotnet/maintenance-packages/releases)
- [Commits](https://github.com/dotnet/maintenance-packages/commits)

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

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

src/PhoneNumbers/PhoneNumbers.csproj

@@ -54,7 +54,7 @@
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="Microsoft.Bcl.HashCode" Version="1.1.1" />
-    <PackageReference Include="System.Memory" Version="4.5.5" />
+    <PackageReference Include="System.Memory" Version="4.6.0" />
   </ItemGroup>
 
   <ItemGroup>