disk_cache: Disable the "List" test for RO disk cache.

It uses a poll function that waits for a second hoping for another thread
to catch up, which is not a reliable way to do synchronization.  The test
has been spuriously failing merges on a regular basis recently.

This is issue #9222, which I'm leaving open until the author can fix the test.

Fixes: 3b69b67545 ("util/fossilize_db: add runtime RO foz db loading via FOZ_DBS_DYNAMIC_LIST")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24755>

src/util/tests/cache_test.cpp

@@ -1016,7 +1016,7 @@ TEST_F(Cache, Combined)
 #endif
 }
 
-TEST_F(Cache, List)
+TEST_F(Cache, DISABLED_List)
 {
    const char *driver_id = "make_check";
    char blob[] = "This is a RO blob";