livepatch: fix delta check for enableByDefault

[lucasmoura]

Why is this needed?

On the process_contract_deltas function, there is a check to see if the entitlement delta has an enableByDefault directive. However, there was a typo on when fetching that value from the delta dict. We are now fixing this typo and adding an unittest for it

Test Steps

check the new unittest for this change

Checklist

• [x] I have updated or added any unit tests accordingly
• [ ] I have updated or added any integration tests accordingly
• [ ] Changes here need to be documented, and this was done in:

Does this PR require extra reviews?

• [ ] Yes
• [x] No

[github-actions[bot]]

Jira: This PR is not related to a Jira item. (The PR title does not include a SC-#### reference)

GitHub Issues: No GitHub issues are fixed by this PR. (No commits have Fixes: #### references)

Launchpad Bugs: No Launchpad bugs are fixed by this PR. (No commits have LP: #### references)

Documentation: The changes in this PR do not require documentation changes.

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