Update release.yml

Author: Lachee

.github/workflows/release.yml

@@ -38,7 +38,9 @@ jobs:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - uses: actions/checkout@v3
       - uses: actions/setup-dotnet@v3
-
+        with:
+          dotnet-version: '3.1.x'
+    
       # Install the packager
       - name: Install Unity Packager
         run: |