Upgrade to dotnet 9

[nicolas63]

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fix #1548
fix #1549

[nicolas63]

hi @Pixel998, I created this PR because, as I explained in the issue, I had already worked(on my fork) on the update before your PR and I still had a unit test problem to correct. As this is your first contribution, I think we can split the bounty in this way 100 for you 400 for me because most of the time is spent on correcting the tests on the blazor side following the update and I also have to do the release, which is why I think this split is fair. What do you think?

[Pixel998]

Hi @nicolas63, I appreciate your offer. I have also spent quite some time and effort on this. I upgraded two codebases, this repository AND jhipster-net repository to fully address the issue. So I hope you can understand this. Thank you.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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