fix: TreeSerializer start pending attr on end/start/attr avents

[tefra]

📒 Description

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Resolves #1024

🔗 What I've Done

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💬 Comments

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🛫 Checklist

• [ ] Updated docs
• [ ] Added unit-tests
• [ ] Sample tests pass
• [ ] W3C tests pass

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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