Ignore corrupt jobs-state.json file

[renanrodrigo]

Why is this needed?

This PR solves all of our problems because we now ignore invalid jobs-state.json files if they are corrupted and cannot be decoded, avoiding the oops which stopped phasing on noble (see LP bug)

LP: #2078737

Test Steps

Unit tests cover behavior for the functionality:

• insert some weird characters in your jobs-state.json file
• systemctl start ua-timer.service
• see it degrade
• apply this patch
• repeat
• see it happy

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• [x] (un)check this to re-run the checklist action

[github-actions[bot]]

PR Checklist

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### Bug References - Launchpad: [#2078737](https://bugs.launchpad.net/ubuntu/+source/ubuntu-advantage-tools/+bug/2078737) #### Confirm - [x] I've properly referenced all bugs that this PR fixes

How to properly reference fixed bugs

* If this PR is related to a Jira item, include an `SC-1234` reference in the PR title * If this PR is fixes a GitHub issue, include a `Fixes: #1234` reference in the commit that fixes the issue * If this PR is fixes a Launchpad bug, include a `LP: #12345678` reference in the commit that fixes the issue

### Test Updates #### Unit Tests - [x] I have updated or added any unit tests accordingly - [ ] No unit test changes are necessary for this change #### Integration Tests - [ ] I have updated or added any integration tests accordingly - [x] No integration test changes are necessary for this change ### Documentation - [ ] Changes here need to be documented and I have referenced the docs PR in the description - [x] No documentation updates are necessary for this change ### Does this PR require review from someone outside the core ubuntu-pro-client team? - [ ] Yes, and I have requested those reviews via GitHub - [x] No

[renanrodrigo]

Ok Github is failing to build the package on Xenial because it is using an outdated version of the Python 3.5 stdlib in the chroot. This is reproducible locally. May have to comment the test out.

[renanrodrigo]

As agreed I just removed the extra unit test (as we never had it anyway) and there is a unit test covering the new exception in the timer job. This is now good to go.