Bump System.Threading.Tasks.Extensions from 4.5.4 to 4.6.0

Bumps [System.Threading.Tasks.Extensions](https://github.com/dotnet/maintenance-packages) from 4.5.4 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.Threading.Tasks.Extensions
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

BitFaster.Caching.UnitTests/BitFaster.Caching.UnitTests.csproj

@@ -23,7 +23,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
-    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.4" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.6.0" />
   </ItemGroup>
 
   <ItemGroup>

BitFaster.Caching/BitFaster.Caching.csproj

@@ -57,7 +57,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-     <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.4" />
+     <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.6.0" />
   </ItemGroup>
 
   <PropertyGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">