update xcopy-msbuild to 16.10.0-preview2

[riarenas]

Brings in the changes from dotnet/arcade-validation@3db6ad5 so that repos can use the new version of the xcopy msbuild compatible with preview 4. Without this change the next arcade update will break repos using the xcopy msbuild.

We have validated this works in an arcadified repo here: https://dev.azure.com/dnceng/internal/_build/results?buildId=1183151&view=results

This should finally fix #7494

• The right tests are in and and the right validation has happened. Guidance: https://github.com/dotnet/core-eng/tree/master/Documentation/Validation

[ghost]

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[ghost]

Apologies, while this PR appears ready to be merged, I've been configured to only merge when all checks have explicitly passed. The following integrations have not reported any progress on their checks and are blocking auto-merge:

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These integrations are possibly never going to report a check, and unblocking auto-merge likely requires a human being to update my configuration to exempt these integrations from requiring a passing check.

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