fix "/etc/apt/sources.list: No such file or directory" error in php-fpm

[star8ks]

Description

Correct source replacing command in php-fpm.
#3492

Motivation and Context

if CHANGE_SOURCE = true, docker will change the source url in /etc/apt/sources.list, but this file does not exist.
Instead, /etc/apt/sources.list.d/debian.sources is the right file to be changed.

Types of Changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).

Definition of Done Checklist:

• I've read the Contribution Guide.
• I've updated the documentation. (refer to this for how to do so).
• I enjoyed my time contributing and making developer's life easier :)