Update branding to 2.1.21 (#23920)

Author: John Luo

Diff for: eng/Baseline.Designer.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
-    <AspNetCoreBaselineVersion>2.1.19</AspNetCoreBaselineVersion>
+    <AspNetCoreBaselineVersion>2.1.20</AspNetCoreBaselineVersion>
   </PropertyGroup>
   <!-- Package: dotnet-dev-certs-->
   <PropertyGroup Condition=" '$(PackageId)' == 'dotnet-dev-certs' ">

Diff for: eng/Baseline.xml

@@ -4,7 +4,7 @@ This file contains a list of all the packages and their versions which were rele
 build of ASP.NET Core 2.1.x. Update this list when preparing for a new patch.
 
 -->
-<Baseline Version="2.1.19">
+<Baseline Version="2.1.20">
   <Package Id="dotnet-dev-certs" Version="2.1.1" />
   <Package Id="dotnet-sql-cache" Version="2.1.1" />
   <Package Id="dotnet-user-secrets" Version="2.1.1" />

Diff for: eng/PatchConfig.props

@@ -66,4 +66,8 @@ Later on, this will be checked using this condition:
       @aspnet/signalr;
     </PackagesInPatch>
   </PropertyGroup>
+  <PropertyGroup Condition=" '$(VersionPrefix)' == '2.1.21' ">
+    <PackagesInPatch>
+    </PackagesInPatch>
+  </PropertyGroup>
 </Project>

Diff for: src/PackageArchive/Archive.CiServer.Patch.Compat/ArchiveBaseline.2.1.20.txt

@@ -0,0 +1 @@
+

Diff for: src/PackageArchive/Archive.CiServer.Patch/ArchiveBaseline.2.1.20.txt

@@ -0,0 +1 @@
+

Diff for: version.props

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <AspNetCoreMajorVersion>2</AspNetCoreMajorVersion>
     <AspNetCoreMinorVersion>1</AspNetCoreMinorVersion>
-    <AspNetCorePatchVersion>20</AspNetCorePatchVersion>
+    <AspNetCorePatchVersion>21</AspNetCorePatchVersion>
     <PreReleaseLabel>servicing</PreReleaseLabel>
     <PreReleaseBrandingLabel>Servicing</PreReleaseBrandingLabel>
     <BuildNumber Condition="'$(BuildNumber)' == '' OR '$(UsingLocalBuildNumber)' == 'true'">t000</BuildNumber>