Disable flag for ClipboardModelTest

With the flag turned on, the 'imageClipData_loadFailure' test is
irrelevant; disabling the flag for now and once the flag is rolled out
the test can be removed.

Flag: EXEMPT fixing test failure
Bug: 357197236
Test: atest ClipboardModelTest
Change-Id: I2ca20fe4810d06a617f107004552c9132ce5c672