Temporary vector layer - same layer gets repeated in Data Sources list

[Fabian Thiel]

Steps to reproduce

• Project → Create Data Source
• New temporary scratch layer
• Add to Map View
• Now, Drag the created Layer from the Data Views into the Map View
• The layer should now show up duplicated in the Data Sources panel
• Repeat, another entry shows up etc.

Version 3.10.0.20220401T124144.develop c7d679b