Kconfig always prompts for saving changes irrespective of wether there was any (IDFGH-16950)

As recently as a couple of months, Kconfig stopped detecting whether any changes to configs were actually made, and prompts for saving configuration regardless. Seems like a regression.

To repro,
1. `idf.py menuconfig`
2. Press `Q` to quit
3. Say `Y` to save configuration
4. Repeat from step 1