Bump StackExchange.Redis from 2.0.601 to 2.1.28

Bumps [StackExchange.Redis](https://github.com/StackExchange/StackExchange.Redis) from 2.0.601 to 2.1.28.
- [Release notes](https://github.com/StackExchange/StackExchange.Redis/releases)
- [Changelog](https://github.com/StackExchange/StackExchange.Redis/blob/master/docs/ReleaseNotes.md)
- [Commits](https://github.com/StackExchange/StackExchange.Redis/commits)

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

Author: dependabot-preview[bot]

src/CacheTower.Extensions.Redis/CacheTower.Extensions.Redis.csproj

@@ -9,7 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="StackExchange.Redis" Version="2.0.601" />
+    <PackageReference Include="StackExchange.Redis" Version="2.1.28" />
   </ItemGroup>
 
   <ItemGroup>

src/CacheTower.Providers.Redis/CacheTower.Providers.Redis.csproj

@@ -10,7 +10,7 @@
 
   <ItemGroup>
     <PackageReference Include="protobuf-net" Version="3.0.0-alpha.103" />
-    <PackageReference Include="StackExchange.Redis" Version="2.0.601" />
+    <PackageReference Include="StackExchange.Redis" Version="2.1.28" />
     <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="4.7.1" />
   </ItemGroup>