TMPro Essentials assets flagged as "missing a signature" when imported on Linux

Steps to reproduce:
1. Create new Unity project
2. Go to Project Settings -> TextMeshPro
3. Click on Import TMPro Essensials
4. Observe the window that appears

Actual result: Editor warns that “These assets are missing a signature”
Expected result: Package is able to be imported with no warnings

Reproducible with: 6000.6.0b6, 6000.7.0a1, 6000.7.0a3
Not reproducible with: 6000.0.80f1, 6000.3.21f1, 6000.5.6f1, 6000.6.0a7

Reproducible on: Ubuntu 24.04
Not reproducible on: MacOS 26.5.2