Update to .NET 9

[mitchelsellers]

Update the project to .NET 9

[sumesh-pu-swg]

@mitchelsellers this project is already in .net 9

[mitchelsellers]

@sumesh-pu-swg I do not see this project as .NET 9.

It is referenced as targeting .NET 8 here - https://github.com/IowaComputerGurus/github-cost-visualizer/blob/main/src/GitHubCostVisualizer.Web/GitHubCostVisualizer.Web.csproj

[mitchelsellers]

Additionally the build runners are actually pushing/validating .NET 6 which should be updated to .NET 9 - https://github.com/IowaComputerGurus/github-cost-visualizer/blob/main/.github/workflows/ci-build.yml