[DocsUI, Search]: Fix testEmptyQueryShowsDirectoryListing

Limits the test to SearchV2, as V1 hides the results behind the past
query view.

Bug: 438732798
Bug: 435522130
Flag: com.android.documentsui.flags.use_search_v2_read_only
Test: atest DocumentsUIGoogleTests
Change-Id: Ic89bf7f43f51136cecb2b1696cfef72d9287cbb7