chore: support preview net8.0

[stijnmoreels]

Support preview version of .NET 8 throughout the libraries, based on preview version of Arcus Observability.

[netlify[bot]]

✅ Deploy Preview for arcus-security canceled.

Name	Link
🔨 Latest commit	544727d87fbda03cb737ac300cacd067f5de866e
🔍 Latest deploy log	https://app.netlify.com/sites/arcus-security/deploys/650d15137834dc0008694d34

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +0.68% :tada:

Comparison is base (d16484a) 89.85% compared to head (7ee288f) 90.53%.

:exclamation: Current head 7ee288f differs from pull request most recent head 544727d. Consider uploading reports for the commit 544727d to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #421 +/- ## ========================================== + Coverage 89.85% 90.53% +0.68% ========================================== Files 20 20 Lines 1065 1057 -8 Branches 82 82 ========================================== Hits 957 957 + Misses 79 71 -8 Partials 29 29 ``` | [Files Changed](https://app.codecov.io/gh/arcus-azure/arcus.security/pull/421?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=arcus-azure) | Coverage Δ | | |---|---|---| | [src/Arcus.Security.Core/SecretNotFoundException.cs](https://app.codecov.io/gh/arcus-azure/arcus.security/pull/421?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=arcus-azure#diff-c3JjL0FyY3VzLlNlY3VyaXR5LkNvcmUvU2VjcmV0Tm90Rm91bmRFeGNlcHRpb24uY3M=) | `58.33% <ø> (+23.33%)` | :arrow_up: |

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[stijnmoreels]

Is everything okay, @fgheysels ? Can we complete this, or did you first want to go over something?