[Material] Shader selection dropdown window flickers in Material.

In Material “Shader” selection dropdown window flickers on clicking shader selection dropdown bar which can be seen easily on multiple clicks.

Steps to repro:
1. Create a new project
2. Project > right-click > Create > Material
3. Material > Inspector > Shader > Shader Dropdown
4. Click multiple times on (standard) Shader selection Dropdown
5. Observe flickering of Shader Dropdown

Actual Result: Shader selection Dropdown window is flickering

Expected Result: Shader selection Dropdown window should not flicker

Reproducible in:
2021.1.0a1, 2020.2.0b8, 2020.1.10f1, 2019.4.10f1, 2018.4.27f1

Environment:
Windows and macOS 10.15