secret-file-backend: Fix use-after-free in flatpak

The on_portal_retrieve_secret() can connect a GCancellable, but it
doesn't disconnect from it (only when the cancellable is cancelled),
which means when the cancellable is cancelled later, when the GTask
is gone, the callback is called with already freed data.
6 jobs for wip/mcrha/flatpak-use-after-free-fix in 5 minutes and 7 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
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passed #634874
fedora:asan

00:03:11

passed #634876
fedora:coverage

00:03:28

69.8%
passed #634875
fedora:ubsan

00:04:44

passed #634873
fedora:Werror

00:03:07

 
  Deploy
passed #634877
pages

00:00:22

passed pages:deploy

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