Draft: ci: update scaffold, add GitLab CI, bump PHPStan to ^2, fix PHPStan 2.x errors

Stuart Clarkrequested to merge
issue/custom_formatters-3592679:feature/3592679-scaffold_update into 4.1.x

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

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