Update core-application.mdx

[cici]

Per ticket EDU-3673, update .NET Task Determinism documentation to be inline with the README.md at https://github.com/temporalio/sdk-dotnet/edit/main/README.md

What does this PR do?

Notes to reviewers

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[cici]

Ready for review @Jwahir Sundai, @brian Macdonald

[brianmacdonald-temporal]

Changes look good.