chore(deps): bump Polyfill from 7.20.0 to 7.21.0 (#315)

Author: dependabot[bot]

Directory.Packages.props

@@ -19,7 +19,7 @@
     <PackageVersion Include="coverlet.msbuild" Version="6.0.4" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageVersion Include="NetEvolve.Extensions.XUnit" Version="2.5.67" />
-    <PackageVersion Include="Polyfill" Version="7.20.0" />
+    <PackageVersion Include="Polyfill" Version="7.21.0" />
     <PackageVersion Include="xunit" Version="2.9.3" />
   </ItemGroup>