Pin third_party/upb to C17. am: 8e1018b031

Original change: https://android-review.googlesource.com/c/platform/external/grpc-grpc/+/3320794

Change-Id: I89d2dda888a544daf7f710e46b7d996b72a27483
Signed-off-by: Automerger Merge Worker <[email protected]>