CI: remote build tests time out when the build queue is busy

[lengau]

Bug Description

When Launchpad's build queue is busy, the remote build tests will time out in CI.

Things we should do in the fix:

1. Modify the init'd charm to only build on & for amd64 (so there's only one build in the queue where Launchpad typically has the most availability)
2. Extend the build time
3. Move the remote build tests to a scheduled weekly test rather than on every PR

To Reproduce

https://github.com/canonical/charmcraft/actions/runs/8096831733/job/22127019796?pr=1560

Environment

CI

charmcraft.yaml

n/a

Relevant log output

n/a

[syncronize-issues-to-jira]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-2565.

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