Update building-and-testing-net.md

[mark-mxwl]

Why:

Closes: #32098

What's being changed (if available, include any code snippets, screenshots, or gifs):

Revised the workflow example to include the updated syntax for setup-dotnet NuGet dependency caching (v3.2.0). As the action uses @toolkit/cache under the hood, there's no need to configure @actions/cache separately. The article has been revised to reflect changes made to the workflow example.

Note: I do wonder if it's necessary to include an installation step in the workflow, as dependency installation is covered the previous section. Thoughts?

Reference material:
Caching NuGet Packages
setup-dotnet v3.2.0

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Source	Preview	Production	What Changed
actions/automating-builds-and-tests/building-and-testing-net.md	fpt ghec ghes@ 3.12 3.11 3.10 3.9	fpt ghec ghes@ 3.12 3.11 3.10 3.9

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ghes: GitHub Enterprise Server

[nguyenalex836]

@mark-mxwl Thanks so much for opening a PR! I'll get this triaged for review ✨

[na1307]

The changes do not mention NuGet lock files. That workflow doesn't work out of the box because generating a NuGet lock file requires modifying the project file.