fix: validate deploy version input

.gitea/workflows/ci.yml

@@ -42,7 +42,9 @@ jobs:
         run: |
           set -euo pipefail
           backend_version="$(sed -n 's/^BACKEND_VERSION = "\(.*\)"$/\1/p' app/version.py)"
-          test -n "$backend_version"
+          case "$backend_version" in
+            ''|*[!0-9.]*) exit 1 ;;
+          esac
           echo "backend_version=$backend_version" >> "$GITHUB_OUTPUT"
           tar --exclude=.git --exclude=.env -cf "$RUNNER_TEMP/$RELEASE_NAME" .
           printf '%s\n' "$PROD_SSH_KEY" > "$RUNNER_TEMP/deploy_key"