Update release notes for 7.4-rc.1

[sdwheeler]

PR Summary

Update release notes for 7.4-rc.1

• Fixes AB#173908

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 70ee9be:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/7.4/Microsoft.PowerShell.Core/About/about_Telemetry.md	✅Succeeded	View (powershell-7.4)
reference/docs-conceptual/install/install-debian.md	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/install/Installing-PowerShell-on-Windows.md	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/install/install-rhel.md	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/install/install-ubuntu.md	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/whats-new/What-s-New-in-PowerShell-74.md	✅Succeeded	View (>=powershell-5.1)

For more details, please refer to the build report.

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