Travis: update the PHP Security Checker

[jrfnl]

Summary

This PR can be summarized in the following changelog entry:

• Safeguard dependency security

Relevant technical choices:

Ref: https://github.com/fabpot/local-php-security-checker/blob/main/CHANGELOG.md

Test instructions

This PR can be tested by following these steps:

• N/A if the build passes we're good