Reproduction steps:
1. Create and open a new Unity project
2. In the "Package Manager" window, add the "Mobile Notifications" package
3. Build the project for iOS (Press "Build", not "Build & Run")
4. Build the Xcode project
5. Repeat steps 3-4, when prompted if you want to replace the Build folder, press "Append"

Expected result: Source files aren't recompiled
Actual result: Source files are recompiled

Reproducible with: Mobile Notifications version 1.3.0 (2018.4.36f1, 2019.4.28f1, 2020.3.12f1, 2021.1.11f1, 2021.2.0a21)