Update .NET version in flowctl-release.yml

Author: ziagham

.github/workflows/flowctl-release.yml

@@ -54,7 +54,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v3.2.0
       with:
-        dotnet-version: 8.0.x
+        dotnet-version: 9.0.x
 
     - name: Prep packages
       run: dotnet nuget add source --username ziagham --password ${{ secrets.GH_TOKEN }} --store-password-in-clear-text --name github "https://nuget.pkg.github.com/${{github.repository_owner}}/index.json"