fix(deps): update netlify build packages

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@netlify/build	^12.19.1 -> ^12.20.0
@netlify/config	^9.4.0 -> ^9.5.0

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Release Notes

netlify/build

v12.20.0

Features

• allow plugins to unset configuration properties (#​3158) (64e1235)

12.19.1 (2021-06-30)

Bug Fixes

• plugins: only rely in the system node version for plugins running Node <10 (#​3144) (74bbff2)

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Configuration

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👻 Immortal: This PR will be recreated if closed unmerged. Get config help if that's undesired.

---

• If you want to rebase/retry this PR, check this box.

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[github-actions]

📊 Benchmark results

Comparing with 4d8c7e7

Package size: 331 MB

(no change)

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• T-16 (4d8c7e7): 331 MB
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• T (current commit): 331 MB