Bump Nuget.packaging to 7.6.0, due to vulnerability.

Author: CartBlanche

MonoGame.Library.BuildScripts.csproj

@@ -38,7 +38,7 @@
   <ItemGroup>
     <PackageReference Include="Cake.FileHelpers" Version="7.0.0" />
     <PackageReference Include="Cake.Frosting" Version="5.0.0" />
-    <PackageReference Include="NuGet.Packaging" Version="6.12.1" />
+    <PackageReference Include="NuGet.Packaging" Version="7.6.0" />
     <PackageReference Include="System.Formats.Asn1" Version="9.0.0" />
   </ItemGroup>