How to reproduce:
1. Open attached project "Regressions2019.3.10.zip" and scene "SampleScene"
2. In Project window, Reimport 'SetTexture' script
3. In Hierarchy window, select 'GameObject' object
4. In Inspector window, right-click on 'SetTexture' script component -> "Set"
5. Observe Console window

Expected result: texture is assigned to the object material, no warnings are thrown
Actual result: warning in console "Property _BaseColor already exists"

Reproducible with: 2019.3.8f1, 2019.4.1f1 (URP 7.3.1), 2020.1.0b12, 2020.2.0a14
Not reproducible with: 2018.4.23f1 (LWRP 4.10.1) 2019.3.0a1, 2019.3.7f1 (URP 7.3.1)
Could not test with:

Notes:
- No repro on MacOS
- No repro with Universal Render Pipeline/Lit shader
- "Set" error only prints to console once per session (reimport 'SetTexture' script)
- Used DX11 when checking
- a similar error prints every time "Set" is clicked if we add Debug.Log(renderer.sharedMaterial.mainTexture);