Fix indentation bug in plugin-loader.php

### Description

When running the configure script, the list of plugins loaded in plugin-loader.php isn't indented properly (needs to be indented one more level).

### Use Case

When a user runs this script, the output should be compatible with our coding standards.

### Acceptance Criteria
- Ensure that when configure.php is run, the resulting output in plugin-loader.php is properly indented.