Fix CI scripts

[Shane32]

Installs missing .NET 8 SDKs

Fixes:

• Add benchmarking #508 (comment)

Hi @Shane32 seems like this PR broke the CI scripts. Can you have a look?
https://github.com/codebude/QRCoder/actions/runs/8884442673/job/24413893321

Run dotnet restore
  dotnet restore
  shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"
  env:
    GH_PKG_SEC: ***
    DOTNET_ROOT: C:\Program Files\dotnet
  Determining projects to restore...
Error: C:\Program Files\dotnet\sdk\7.0.[4](https://github.com/codebude/QRCoder/actions/runs/8884442673/job/24413893321#step:4:4)08\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.TargetFrameworkInference.targets(160,[5](https://github.com/codebude/QRCoder/actions/runs/8884442673/job/24413893321#step:4:5)): error NETSDK1045: The current .NET SDK does not support targeting .NET 8.0.  Either target .NET [7](https://github.com/codebude/QRCoder/actions/runs/8884442673/job/24413893321#step:4:8).0 or lower, or use a version of the .NET SDK that supports .NET [8](https://github.com/codebude/QRCoder/actions/runs/8884442673/job/24413893321#step:4:9).0. Download the .NET SDK from https://aka.ms/dotnet/download [D:\a\QRCoder\QRCoder\QRCoderBenchmarks\QRCoderBenchmarks.csproj]
Error: Process completed with exit code 1.

Originally posted by @codebude in #508 (comment)