Bump to stable 1.28.0

Author: kamilchodola

src/Nethermind/Directory.Build.props

@@ -15,7 +15,7 @@
     <Product>Nethermind</Product>
     <SourceRevisionId Condition="'$(Commit)' != ''">$(Commit)</SourceRevisionId>
     <VersionPrefix>1.28.0</VersionPrefix>
-    <VersionSuffix>rc</VersionSuffix>
+    <VersionSuffix></VersionSuffix>
   </PropertyGroup>
 
   <ItemGroup Label="AssemblyCustomMetadata">