Fix checkout action version

Author: un-def

.github/workflows/release.yml

@@ -69,7 +69,7 @@ jobs:
     needs: [set-version, build]
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@6
+    - uses: actions/checkout@v6
     - uses: actions/download-artifact@v8
       with:
         name: dstack-sshproxy