getInterfaceDescription: Fix rclcpp API breakage

[JafarAbdi]

Description

ros2/rclcpp@679fb2b broke the API for async_send_request, so using response.get() multiple times will throw an exception std::future_error "No associated state"

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

Merging #686 (2b07fed) into main (0b27304) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #686   +/-   ##
=======================================
  Coverage   54.17%   54.17%           
=======================================
  Files         192      192           
  Lines       20182    20182           
=======================================
  Hits        10931    10931           
  Misses       9251     9251           

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[sjahr]

I've built and tested it and everything worked