manifest: use alt image

[incognitojam]

• [x] push images so test passes
• [x] erase partition before flashing skip chunks image

[incognitojam]

tested once using https://github.com/commaai/openpilot/pull/29468 manifest, flashed successfully

EDIT: getting the weird Scanning for networks no wi-fi results like when the cache partition was erased

[incognitojam]

currently checksum fails when running flash- will add a test for this too

[incognitojam]

testing flashing device again and worked fine - test is quite slow to download and calculate the checksum. (testing CI speed now)