fix: correct env var name for Fastlane in TestFlight upload step

[Ghostmonday]

Problem

Fastlane's app_store_connect_api_key_from_env reads APP_STORE_CONNECT_API_KEY_P8_BASE64 directly from the environment (Fastfile line 17):

But the Upload step was passing APP_STORE_CONNECT_API_KEY instead — causing:

Fix

Rename APP_STORE_CONNECT_API_KEY → APP_STORE_CONNECT_API_KEY_P8_BASE64 in the Upload step env block, matching what the Fastfile expects.