Bump Microsoft.NETFramework.ReferenceAssemblies and System.Threading.Tasks.Extensions

Bumps [Microsoft.NETFramework.ReferenceAssemblies](https://github.com/Microsoft/dotnet) and [System.Threading.Tasks.Extensions](https://github.com/dotnet/maintenance-packages). These dependencies needed to be updated together.

Updates `Microsoft.NETFramework.ReferenceAssemblies` from 1.0.3 to 1.0.3
- [Commits](https://github.com/Microsoft/dotnet/commits)

Updates `System.Threading.Tasks.Extensions` from 4.5.4 to 4.6.3
- [Release notes](https://github.com/dotnet/maintenance-packages/releases)
- [Commits](https://github.com/dotnet/maintenance-packages/commits)

---
updated-dependencies:
- dependency-name: Microsoft.NETFramework.ReferenceAssemblies
  dependency-version: 1.0.3
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: System.Threading.Tasks.Extensions
  dependency-version: 4.6.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

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="4.6.3" />
   </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="4.6.3" />
   </ItemGroup>
 
   <PropertyGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">