fix: content/actions/creating-actions/dockerfile-support-for-github-actions.md to reduce vulnerabilities (#98)

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

Author: snyk-bot

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

@@ -67,7 +67,7 @@ ENTRYPOINT ["sh", "-c", "echo $GITHUB_SHA"]
 
 ```dockerfile
 # Container image that runs your code
-FROM debian:9.13-slim
+FROM debian:10.12-slim
 
 # Copies your code file from your action repository to the filesystem path `/` of the container
 COPY entrypoint.sh /entrypoint.sh