Added support for .NET Framework 4.8.1 (#9327)

* Added support for .NET Framework 4.8.1

* test CI

* Revert "test CI"

Author: advay26

src/NuGetGallery.Core/Frameworks/SupportedFrameworks.cs

@@ -25,6 +25,7 @@ public static class SupportedFrameworks
         public static readonly NuGetFramework MonoTouch = new NuGetFramework(FrameworkIdentifiers.MonoTouch, EmptyVersion);
         public static readonly NuGetFramework MonoMac = new NuGetFramework(FrameworkIdentifiers.MonoMac, EmptyVersion);
         public static readonly NuGetFramework Net48 = new NuGetFramework(FrameworkIdentifiers.Net, new Version(4, 8, 0, 0));
+        public static readonly NuGetFramework Net481 = new NuGetFramework(FrameworkIdentifiers.Net, new Version(4, 8, 1, 0));
         public static readonly NuGetFramework Net50Windows = new NuGetFramework(FrameworkIdentifiers.NetCoreApp, Version5, "windows", EmptyVersion);
         public static readonly NuGetFramework Net60Android = new NuGetFramework(FrameworkIdentifiers.NetCoreApp, Version6, "android", EmptyVersion);
         public static readonly NuGetFramework Net60Ios = new NuGetFramework(FrameworkIdentifiers.NetCoreApp, Version6, "ios", EmptyVersion);
@@ -57,7 +58,7 @@ static SupportedFrameworks()
             {
                 MonoAndroid, MonoMac, MonoTouch,
                 Native,
-                Net11, Net2, Net35, Net4, Net403, Net45, Net451, Net452, Net46, Net461, Net462, Net463, Net47, Net471, Net472, Net48,
+                Net11, Net2, Net35, Net4, Net403, Net45, Net451, Net452, Net46, Net461, Net462, Net463, Net47, Net471, Net472, Net48, Net481,
                 Net50, Net50Windows,
                 Net60, Net60Android, Net60Ios, Net60MacCatalyst, Net60MacOs, Net60TvOs, Net60Windows,
                 Net70, Net70Android, Net70Ios, Net70MacCatalyst, Net70MacOs, Net70TvOs, Net70Windows,