Fix coverage parsing for projects that use namespaces

[DaDummy]

In projects with more than one namespace the coverage was not correctly parsed.

Having multiple namespaces resulted in the following hierarchy being output by the XMLParser:

{
    "node": {
        "?xml": {
            "@_version": "1.0",
            "@_encoding": "UTF-8"
        },
        "coverage": {
            "project": {
                "package": [
                    {
                        "file": {
                            /* ... */
                        }
                    },
                    {
                        "file": [
                            {
                                /* ... */
                            }
                        ]
                    }
                ]
            }
        }
    }
}

This was not correctly handled by querySelectorAll, which assumed that only the innermost selected node could be an array.

This MR corrects that.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.42%. Comparing base (cdc47bf) to head (4e8d671).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/PHPUnit/Element.ts	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #337      +/-   ##
==========================================
- Coverage   95.52%   95.42%   -0.11%     
==========================================
  Files          60       60              
  Lines        4516     4520       +4     
  Branches     1012     1012              
==========================================
- Hits         4314     4313       -1     
- Misses        197      203       +6     
+ Partials        5        4       -1     

Flag	Coverage Δ
unittests	95.33% <80.00%> (-0.16%)	⬇️

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[DaDummy]

The observed issue and new code should now be covered in the tests