[aspnetcore] Fix swagger xml comments

[david-marconis]

This fixes issue #19592. Tested by building and applying the fix to the example given in the issue and verified working.
Steps ran from the failure state in the issue (present in sibling directory, hence ../):

java -jar ../openapi-generator/modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -g aspnetcore -i openapi.yaml
dotnet test src/Org.OpenAPITools.Tests

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[wing328]

thanks for the PR

let's give it a try