Update AggregateException.xml

[epsitec]

Related to https://github.com/dotnet/runtime/pull/107743

Summary

Fixes an incorrect description of what method GetBaseException() does.

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Tagging subscribers to this area: @dotnet/area-system-runtime

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Learn Build status updates of commit 0d6d7e9:

:warning: Validation status: warnings

File	Status	Preview URL	Details
xml/System/AggregateException.xml	:warning:Warning	View	Details

xml/System/AggregateException.xml

• Line 0, Column 0: [Warning: xref-not-found - See documentation] Cross reference not found: 'Exception'.
• Line 0, Column 0: [Warning: xref-not-found - See documentation] Cross reference not found: 'AggregateException'.

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

Learn Build status updates of commit 4f513d6:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
xml/System/AggregateException.xml	:white_check_mark:Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
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