How to reproduce:
1. Open the user-attached project (U.AutoCopyFiles.zip)
2. Enable "Parallel Import" in: Project Settings > Editor > Asset Pipeline
3. Open the system's terminal in "[Project Path]/Assets/AutoCopyFiles"
4. Run: $python3 ./test.py
5. Return to the Editor
6. Press Ctrl+K to open the Quick Search window to start indexing the assets
7. Open the System Monitor and observe Unity's memory usage
Expected result: the Quick Search successfully indexes all the assets and doesn't run out of memory
Actual result: the Editor runs out of memory (the Editor may also crash)

Reproducible with: 2021.3.8f1

Reproducible on: Ubuntu 18.04, Ubuntu 20.04

Note: the issue is not reproducible 100% of the time and not on all Linux setups