Update .NET version to 9.0.x in workflows

Upgraded the .NET version from 6.0.x to 9.0.x in the
GitHub Actions workflows across `engine_assets_tpk.yml`,
`test.yml`, and `type_tree_tpk.yml` for improved build
process compatibility.

Author: ds5678

.github/workflows/engine_assets_tpk.yml

@@ -31,7 +31,7 @@ jobs:
      - name: Setup .NET
        uses: actions/setup-dotnet@v4
        with:
-         dotnet-version: 6.0.x
+         dotnet-version: 9.0.x
      - name: Build
        run: dotnet build /p:Configuration=Release
        working-directory: ./Tpk.ConsoleApp/

.github/workflows/test.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 6.0.x
+        dotnet-version: 9.0.x
     - name: Restore dependencies
       run: dotnet restore
     - name: Build

.github/workflows/type_tree_tpk.yml

@@ -31,7 +31,7 @@ jobs:
      - name: Setup .NET
        uses: actions/setup-dotnet@v4
        with:
-         dotnet-version: 6.0.x
+         dotnet-version: 9.0.x
      - name: Build
        run: dotnet build /p:Configuration=Release
        working-directory: ./Tpk.ConsoleApp/