docs: Fixing typo (i.e without closing period)

The CommonTypos linter complained about "i.e" without a closing period.
Since our tech writing style guide says to avoid "i.e." in general, I
rephrased as "that is".

Per go/fix-refdocs, tm-qpr-dev is now the preferred branch for doc fixes
until the U dev branch is open. Since this CL hasn't been reviewed yet,
I'm CPing it over here and abandoning the original CL.

Docs-only change, no change to code.

Change-Id: Id8de0d371e1290a7e8ed1831f2fbca063f9ff835
Test: [go/abtd docs build]
Bug: 263824202