Partial failure of Cancel button

[DonEdwards]

Describe the bug
Clicking Cancel button on the password form, or while apt packages are downloading, does not cancel flatpak updates.

Steps to reproduce
Steps to reproduce the behavior:

1. Run mintUpdate and get a list that includes flatpaks with available updates.
2. Click the button to begin the update process.
   3a. On the password form, click Cancel.
   4a. Watch the flatpaks get updated anyway.
   --- or --
   3b. Enter password.
   4b. While apt packages are downloading, click Cancel.
   5b. Watch the flatpaks get updated anyway.

Expected behavior
The Cancel button should cleanly terminate the update process. Not just terminate the current stage and move to the next stage.

Distribution:

• [* ] Linux Mint

Software version:
mintUpdate 7.1.4

Additional context
I haven't tried the Cancel button during flatpak downloads. That should be checked too, I think, and should stop updates that have not been completely downloaded and applied.