Mark testCopyDirRecursively_loadingInFirstCursor as large

This test is sometimes observed to take over 1 minute to run, causing
failures in presubmit, so mark it accordingly.

Bug: 426030627
Test: atest -c 'DocumentsUIGoogleTests:com.android.documentsui.services.CopyJobTest'
Flag: TEST_ONLY
Change-Id: I94564f1c58a336d933f57ecfe6787eeed4019a69