The package dependencies list in the package manager window allows editing the text like 'Cut', 'Copy' & 'Paste'.
Refer to the attached Video.

Steps to Reproduce:
1. Create a New Project
2. Window > Package Manager
3. Any Package > Dependencies List > Select
4. Enter or paste any text

Actual Result:
Package Dependencies Text is editable

Expected Result:
Package Dependencies Text should not allow editing except "Copy"

Occurring on:
2020.2.0a1, 2020.1.0a25, 2020.1.0a21

Working Fine on:
2020.1.0a20, 2019.3.3f1

Environment:
Both windows 10 and macOS 10.14, 10.15

License type: Pro