Update references to 7.3

[sdwheeler]

PR Summary

Update references to 7.3

• Fixes AB#250373

  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.
• [x] Contributor's Guide: I have read the contributors guide.
• [x] Style: This PR adheres to the style guide.

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

Learn Build status updates of commit 4f63e7a:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/how-to-use-docs.md	:white_check_mark:Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/install/PowerShell-Support-Lifecycle.md	:white_check_mark:Succeeded	View (>=powershell-5.1)

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