[io] Update fallback root certificates.

Change-Id: If1a296bfbf504d96286c275d8cb5978e4270adab
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/397700
Reviewed-by: Brian Quinlan <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google