fix: translations/ja-JP/content/actions/creating-actions/dockerfile-support-for-github-actions.md to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DEBIAN9-DPKG-2847943
- https://snyk.io/vuln/SNYK-DEBIAN9-GCC6-347562
- https://snyk.io/vuln/SNYK-DEBIAN9-SYSTEMD-546478
- https://snyk.io/vuln/SNYK-DEBIAN9-SYSTEMD-546478
- https://snyk.io/vuln/SNYK-DEBIAN9-ZLIB-2433935

Author: snyk-bot

translations/ja-JP/content/actions/creating-actions/dockerfile-support-for-github-actions.md

@@ -62,7 +62,7 @@ ENTRYPOINT ["sh", "-c", "echo $GITHUB_SHA"]
 ##### *Dockerfile*の例
 ``` 
 # コードを実行するコンテナイメージ
-FROM debian:stretch-20211201-slim
+FROM debian:9-slim
 
 # アクションリポジトリからコンテナのファイルシステムパスの`/`にコードファイルをコピー
 COPY entrypoint.sh /entrypoint.sh