Minor: Fix f-strings in Quadplane SimBatteryResistance test

[hunt0r]

Summary

Tiny fix to autotest output strings, no changes to code or test behavior.

Also, by default ~10 decimals were unnecessarily printed. So now print only 4 decimal places.

Classification & Testing (check all that apply and add your own)

• Checked by a human programmer
• Non-functional change
• No-binary change
• Infrastructure change (e.g. unit tests, helper scripts)
• Automated test(s) verify changes (e.g. unit test, autotest)
• Tested manually, description below (e.g. SITL)
• Tested on hardware
• Logs attached
• Logs available on request

(Found these while working on something else, the number now prints as expected.)

[peterbarker]

Good when CI passes.

We're being a bit stricter on our subsystem names now.