fix: 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-LIBGCRYPT20-1582895
- https://snyk.io/vuln/SNYK-DEBIAN9-LZ4-1277599
- https://snyk.io/vuln/SNYK-DEBIAN9-SYSTEMD-546478
- https://snyk.io/vuln/SNYK-DEBIAN9-TAR-312293
- https://snyk.io/vuln/SNYK-DEBIAN9-ZLIB-2433935

Author: snyk-bot

content/actions/creating-actions/dockerfile-support-for-github-actions.md

@@ -66,7 +66,7 @@ ENTRYPOINT ["sh", "-c", "echo $GITHUB_SHA"]
 
 ```dockerfile
 # Container image that runs your code
-FROM debian:stretch-20210408-slim
+FROM debian:stretch-20220418-slim
 
 # Copies your code file from your action repository to the filesystem path `/` of the container
 COPY entrypoint.sh /entrypoint.sh