Fix package source mapping keys in temp config file For packing-common

[v-dmerugu]

Description

NuGet Package Source Mapping enforces that a package's declared source in must match a corresponding source name under .
The Azure Pipelines internal NuGet helper (NuGetConfigHelper2.ts) currently prefixes internal feed names with feed- when writing the temporary NuGet.config used during restore,
However, the helper does not update the section accordingly, leaving the mapping with the original key:

NuGet interprets this mismatch as a violation of Package Source Mapping rules and fails with:

NU1100: PackageSourceMapping is enabled, the following source(s) were not considered: feed-canarytest

📌 Bug 2340656: DotNetCoreCLI@2 breaks package source mappings for internal feeds when using a nuget.config file

Keeps existing feed prefixing untouched (feed- logic stays exactly as before).
Tracks original → prefixed feed names when internal sources are rewritten.
After the temp NuGet.config is generated, the fix:
Loads the XML,
Locates ,
Updates mapping keys to match their prefixed feed names, e.g.: canarytest → feed-canarytest
Writes back the corrected temporary config.

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Package Name

packaging-common

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Risk Assessment (Low / Medium / High)

Low - Only modifies temporary NuGet.config used during restore and doesnot modify prefixing logic or authentication logic.

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Unit Tests Added or Updated

• Unit tests added or updated
• Manual tests performed

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Additional Testing Performed

Tested Manually by uploading changes to private org - https://dev.azure.com/v-dmerugu0683/Sample%20Project/_build/results?buildId=1023&view=logs&j=4ef10708-f316-5e1d-20e0-afbca60c92cd&t=77245893-7256-55ca-6acf-ef97785d1a31

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Documentation Changes Required (Yes / No)

yes - https://learn.microsoft.com/en-us/nuget/consume-packages/package-source-mapping

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Related Issues

microsoft/azure-pipelines-tasks#21507

Checklist

• Related issue linked (if applicable)
• Package version was bumped — see versioning guide
• Verified the package behaves as expected
• CLA signed (if applicable) — see Contributor License Agreement

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[v-dmerugu]

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