[Security] Workflow main.yml is using vulnerable action actions/checkout

The workflow main.yml is referencing action actions/checkout using references v1. However this reference is missing the commit [a6747255bd19d7a757dbdda8c654a9f84db19839](https://github.com/actions/checkout/commits/a6747255bd19d7a757dbdda8c654a9f84db19839) which may contain fix to the some vulnerability.
The vulnerability fix that is missing by actions version could be related to:
(1) CVE fix
(2) upgrade of vulnerable dependency
(3) fix to secret leak and others.
Please consider to update the reference to the action.