Fix a few typos

[real-guanyuming-he]

PR Summary

Fix a few typos in three documentations.

1. reference/docs-conceptual/community/contributing/pull-requests.md
2. reference/docs-conceptual/dsc/overview.md
3. reference/docs-conceptual/security/security-features.md

PR Checklist

• [x] Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• [x] Summary: This PR's summary describes the scope and intent of the change.
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• [x] Style: This PR adheres to the style guide.

[real-guanyuming-he]

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[learn-build-service-prod[bot]]

Learn Build status updates of commit 8835470:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/community/contributing/pull-requests.md	:white_check_mark:Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/dsc/overview.md	:white_check_mark:Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/security/security-features.md	:white_check_mark:Succeeded	View (>=powershell-5.1)

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[github-actions[bot]]

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