Fix to prevent stderr warnings from creating error annotations on successful installations

[lmvysakh]

Description:
Code fix to properly address errors and warnings.

1. Buffer stderr lines during execution instead of logging them immediately.
2. After the installation script exits, check the exit code to determine log severity:
   • Exit code ≠ 0 → log stderr lines with core.error() (red annotations - genuine failure)
   • Exit code = 0 → log stderr lines with core.warning() (yellow annotations - informational warning)