[electrum] Increase the timeout for entering the bootloader mode

Summary: Bump from 30s to 60s. 30s can be a bit short on windows where the USB connection takes time, plus the time the user has to wait for the screen to become responsive and figure out where to click.

Test Plan: Run an upgrade.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17843