Update the `PackageReference` for `OpenTK` to 4.8.0.

[mathew-odwyer]

Description

I propose we update the PackageReference for OpenTK to 4.8.0 as it is the latest stable release.

GLWpfControl/src/GLWpfControl/GLWpfControl.csproj

Line 11 in 516bf69

<PackageReference Include="OpenTK" Version="4.7.5" />

We should also likely update the paket?

GLWpfControl/src/GLWpfControl/paket

Line 26 in 516bf69

OpenTK ~> 4.0 >= 4.3.0

The Why

This will hopefully resolve an issue where users are referencing GLWpfControl and getting a NU1608 warning about the current reference of OpenTK needing to be fixed.

However, I'm a little confused because the NuGet package dependencies show >= 4.3.0 && < 5.0.0

The How

I believe just updating the PackageReference and uploading a new package with the correct constraints should fix this issue.

[NogginBops]

I think that maybe the paket line should be OpenTK ~> 4 >= 4.8.0? So that it becomes >= 4.8.0 && < 5.0.0, but I'm not 100% sure.

[NogginBops]

Fixed with #86