PHPStan job fails while there is no PHP files to scan

Migrated issue

Reported by: grimreaper

Related to !175 (merged) !171 (merged)

Problem/Motivation

In https://git.drupalcode.org/issue/sobki_theme_admin-3436970/-/jobs/1201441, PHPStan job is failing while there is currently no PHP files (*.php, *.theme, etc.) in the theme.

Proposed resolution

Remaining tasks

API changes

Related issue: Issue #3437397