Update TFM to .NET 9.0 and create shared dotnet setup action for workflows

[Copilot]

• Create global.json file with .NET 9.0 SDK version
• Update TFM in ListingManager.csproj from net8.0 to net9.0
• Update TFM in ListingManager.Tests.csproj from net8.0 to net9.0
• Create shared composite action for setup-dotnet in workflows
• Update build-and-test.yml to use shared action with global.json
• Update deploy.yml to use shared action with global.json
• Verify all tests pass with .NET 9.0 (71/77 passing - same as before)
• Verify packing continues to work with .NET 9.0 (successfully creates nupkg with net9.0 tools)
• Fix global.json to use version 9.0.100 (base SDK version) instead of 9.0.0 which doesn't exist

Original prompt

Update TFM to .net9.0 and global.json to .net 9.0 - make sure all tests and packing continue to work.

In all workflows, make a shared action for setting up dotnet, in which instead of hard coding the .net version, let it target the global.json file

• uses: actions/setup-dotnet@v5
  with:
  global-json-file: csharp/global.json

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[BenjaminMichaelis]

@copilot

Exception: D:\a_actions\actions\setup-dotnet\v5\externals\install-dotnet.ps1:1319
Line |
1319 | throw "Could not find "$assetName" with version = $($DownloadLi …
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| Could not find ".NET Core SDK" with version = 9.0.0 Refer to: https://aka.ms/dotnet-os-lifecycle for information
| on .NET support
Error: Failed to install dotnet, exit code: 1. dotnet-install: Downloading from "primary" link has failed with error:

[Copilot]

@copilot

Exception: D:\a_actions\actions\setup-dotnet\v5\externals\install-dotnet.ps1:1319
...

Fixed in commit 4b32f0e. Changed global.json to use version 9.0.100 instead of 9.0.0. The version 9.0.0 doesn't exist - the base SDK version for .NET 9 is 9.0.100, and with rollForward: latestMinor it will use the latest available patch version.