Update workflows to use .NET 9

Author: magahl-swegon

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v3
         with:
-          dotnet-version: 8.0.x
+          dotnet-version: 9.0.x
       - name: Restore dependencies
         run: dotnet restore
       - name: Build

.github/workflows/docs.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Setup .NET Core
         uses: actions/setup-dotnet@v3
         with:
-          dotnet-version: 8.0.x
+          dotnet-version: 9.0.x
 
       - name: Publish
         working-directory: docs/Linq2GraphQL.Docs

.github/workflows/release.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v2
         with:
-          dotnet-version: 8.0.x
+          dotnet-version: 9.0.x
 
       - uses: dotnet/nbgv@master
         id: nbgv