libnmc-base/utils: Improve qr code bottom border
Summary
Use Upper Half Block to show the bottom of the QR code generated
Purpose
The bottom border of the generated QR code had a different thickness compared to other borders.
Improve it by using Upper Half Block so that all borders have similar thickness.
Checklist
Please read https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/main/CONTRIBUTING.md before opening the merge request. In particular, check that:
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the subject for all commits is concise and explicative -
the message for all commits explains the reason for the change -
the source is properly formatted -
any relevant documentation is up to date -
you have added unit tests if applicable