Only add async for x-google-lro

[slevenick]

Check for the x-google-lro extension instead of assuming LROs exist

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

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Your PR hasn't generated any diffs, but I'll let you know if a future commit does.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR hasn't generated any diffs, but I'll let you know if a future commit does.

[rileykarson]

Hey! I'm closing this PR as a part of a cleanup of older inactive PRs, using a threshold of PRs last updated over 3 months ago. This doesn't represent rejection of the change, and feel free to comment for me to reopen it if you plan to pick it back up, or feel free to start a new PR with the same changes in the future.