Fix TODO in CannotAddOrRemoveVirtualKeyword

[krwq]

There is a TODO in this file which says that we should fix it when rules are established. Mentioned issue is now fixed.

sdk/src/Compatibility/ApiCompat/Microsoft.DotNet.ApiCompatibility/Rules/CannotAddOrRemoveVirtualKeyword.cs

Line 72 in adbbd10

// TODO: This check can be expanded once compatibility rules for

Ref: #26169

We should do investigation if any work is required, if not: remove TODO. Changes should be minimal and focus on correctness.

[dotnet-policy-service]

@dotnet/area-infrastructure-libraries a new issue has been filed in the ApiCompat area, please triage