Update release notes for 7.5-preview.3

[sdwheeler]

PR Summary

Update release notes for 7.5-preview.3

• Fixes AB#255484

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
• Contributor's Guide: I have read the contributors guide.
• Style: This PR adheres to the style guide.

[learn-build-service-prod]

Learn Build status updates of commit e277e86:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/7.5/Microsoft.PowerShell.Core/About/about_Tab_Expansion.md	✅Succeeded	View (powershell-7.5)
reference/7.5/Microsoft.PowerShell.Utility/ConvertTo-Json.md	✅Succeeded	View (powershell-7.5)
reference/docs-conceptual/whats-new/What-s-New-in-PowerShell-75.md	✅Succeeded	View (>=powershell-5.1)

For more details, please refer to the build report.

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