Fix typo on rust caching section

[mdevino]

Why:

There was a typo in the documentation.

Closes: I didn't raise an issue, but I could if needed.

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

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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actions/use-cases-and-examples/building-and-testing/building-and-testing-rust.md	fpt ghec ghes@ 3.16 3.15 3.14 3.13 3.12	fpt ghec ghes@ 3.16 3.15 3.14 3.13 3.12

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[Sharra-writes]

Thanks so much for opening a PR! I'll get this triaged for review.

[subatoi]

Many thanks for your help, @mdevino! I'll get this merged now

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