Fix PHPStan: drop dead null-coalesce in XlsxFileInterpreter::getWorksheetInfo()

[jcPimcore]

Problem

After #661 merged, static analysis on 2026.2 started failing (https://github.com/pimcore/data-importer/actions/runs/31784862881) across all PHPStan matrix jobs:

Offset 'worksheetName' on array{worksheetName: string, lastColumnLetter: string, lastColumnIndex: int, totalRows: int, totalColumns: int, sheetState: string} on left side of ?? always exists and is not nullable.
Offset 'totalRows' on array{...} on left side of ?? always exists and is not nullable.
Offset 'lastColumnLetter' on array{...} on left side of ?? always exists and is not nullable.

PhpOffice\PhpSpreadsheet\Reader\IReader::listWorksheetInfo() is typed to always return worksheetName, lastColumnLetter, and totalRows as non-nullable. The ?? null / ?? 0 / ?? 'A' fallbacks added in XlsxFileInterpreter::getWorksheetInfo() in #661 are therefore unreachable dead code, which PHPStan (highest level) flags.

Fix

Drop the dead fallbacks and the now-unnecessary casts. No behavior change — these branches were never reachable.

Testing

No regression test added: this is a static-analysis-only fix with no functional change, so there is nothing to regression-test. Not verified locally (no PHP/Composer/PHPStan available in the environment this was prepared in) — CI on this PR is the verification.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

Pull request overview

Removes unreachable fallbacks in XLSX worksheet metadata handling to restore PHPStan compliance without changing behavior.

Changes:

• Access required worksheet metadata directly.
• Remove redundant casts and null-coalescing defaults.

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