fix: jobs encryption spec key name fix

[jsilva]

Describe your changes

Fixing casting bug in job manifest serialisation

Issue ticket number and link

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] If it is a core feature, I have added thorough tests.

[codecov-commenter]

Codecov Report

Base: 72.01% // Head: 72.01% // No change to project coverage :thumbsup:

Coverage data is based on head (2da172d) compared to base (a786c73). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #48 +/- ## ======================================= Coverage 72.01% 72.01% ======================================= Files 55 55 Lines 2562 2562 ======================================= Hits 1845 1845 Misses 717 717 ``` | [Impacted Files](https://codecov.io/gh/avast/wanna-ml/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=avast) | Coverage Δ | | |---|---|---| | [src/wanna/core/services/jobs.py](https://codecov.io/gh/avast/wanna-ml/pull/48/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=avast#diff-c3JjL3dhbm5hL2NvcmUvc2VydmljZXMvam9icy5weQ==) | `77.24% <ø> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=avast). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=avast)

:umbrella: View full report at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.