Fix mismatched paramrefs (System.T*)

[gewarren]

Contributes to #10183

(Hide whitespace changes.)

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-text-encoding

[learn-build-service-prod]

Learn Build status updates of commit 2e6a110:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Text.RegularExpressions/GroupCollection.xml	✅Succeeded	View
xml/System.Text/ASCIIEncoding.xml	✅Succeeded	View
xml/System.Text/Decoder.xml	✅Succeeded	View
xml/System.Text/Encoding.xml	✅Succeeded	View
xml/System.Text/EncodingProvider.xml	✅Succeeded	View
xml/System.Text/Rune.xml	✅Succeeded	View
xml/System.Text/StringBuilder.xml	✅Succeeded	View
xml/System.Text/UnicodeEncoding.xml	✅Succeeded	View
xml/System.Text/UTF32Encoding.xml	✅Succeeded	View
xml/System.Text/UTF7Encoding.xml	✅Succeeded	View
xml/System.Text/UTF8Encoding.xml	✅Succeeded	View
xml/System.Threading.Tasks/Task.xml	✅Succeeded	View
xml/System.Threading/LazyThreadSafetyMode.xml	✅Succeeded	View
xml/System.Threading/ReaderWriterLock.xml	✅Succeeded	View
xml/System.Threading/ThreadPool.xml	✅Succeeded	View
xml/System.Transactions/TransactionManager.xml	✅Succeeded	View

For more details, please refer to the build report.

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[BillWagner]

This LGTM @gewarren

Let's