Backport of #26290 to release/v7.6

Triggered by @TravisEz13 on behalf of @daxian-dbw

Original CL Label: CL-BuildPackaging

/cc @PowerShell/powershell-maintainers

Impact

REQUIRED: Choose either Tooling Impact or Customer Impact (or both). At least one checkbox must be selected.

Tooling Impact

• Required tooling change
• Optional tooling change (include reasoning)

Fixes Start-PSBuild to correctly handle ready-to-run compilation based on configuration. Previously Debug builds incorrectly enabled ready-to-run, making debugging impossible. This fix ensures developers can properly debug PowerShell on release/v7.6 branch.

Customer Impact

• Customer reported
• Found internally

Regression

REQUIRED: Check exactly one box.

• Yes
• No

This is not a regression.

Testing

Original PR verified that Start-PSBuild correctly enables ready-to-run only for Release configuration. Backport tested by:

1. Building with Debug configuration and confirming ready-to-run is disabled
2. Building with Release configuration and confirming ready-to-run is enabled
3. Verifying debugging capability works in Debug builds

Risk

REQUIRED: Check exactly one box.

• High
• Medium
• Low

Medium risk: Changes build configuration properties that affect all deployments (FxDependentDeployment and SelfContained). The change is well-scoped to only add Configuration conditions, preserving existing behavior for Release builds while fixing Debug builds. Has been validated in master branch.