DocsUI: Update test target SDK version to match the app

This is an attempt to fix the message:
"This app isn't compatible with the latest version of Android. Check
for an update or contact the app's developer"

Bug: 428788305
Flag: EXEMPT test code
Test: atest DocumentsUIGoogleTests
Change-Id: Ibfd44f0ce8293c9fab7e51fa2341d7eb1c4ffca0