(GH-10452) Improve here-string example

[michaeltlombardi]

PR Summary

Prior to this change, the example for demonstrating how a here-string can simplify syntax defined a value that would've been valid even in a normal double-quoted string.

This change:

• Updates the example to use both a single quote and a double quote, which would require escaping in a normal string, to make the usage and value clearer.
• Addresses error-level issues for the document's prose style.
• Resolves Example for here-string in About_Quoting_Rules could be better #10452
• Fixes AB#163608

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 19a1ce6:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/5.1/Microsoft.PowerShell.Core/About/about_Quoting_Rules.md	✅Succeeded	View (powershell-5.1)
reference/7.2/Microsoft.PowerShell.Core/About/about_Quoting_Rules.md	✅Succeeded	View (powershell-7.2)
reference/7.3/Microsoft.PowerShell.Core/About/about_Quoting_Rules.md	✅Succeeded	View (powershell-7.3)
reference/7.4/Microsoft.PowerShell.Core/About/about_Quoting_Rules.md	✅Succeeded	View (powershell-7.4)

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