docs: Typo fix in TextLinks.Request.Builder

Needed to edit the Android code to test out the "fix a reference doc
bug" instructions, so I looked for a typo I could fix.

NO_TEST , fixes a doc bug (no code edits).

Change-Id: I19ffc5e5fdaf3e6b046ce2e5c34ca034c3b6c6e4
Test: [go/abtd docs build]
Fixes: 269786320