ci: disable a flaky test

Signed-off-by: Andrea Terzolo <andreaterzolo3@gmail.com>

userspace/libsinsp/test/async_key_value_source.ut.cpp

@@ -335,8 +335,15 @@ TEST(async_key_value_source_test, look_key_delayed_async_callback) {
 
 /**
  * Ensure that "old" results are pruned
+ * This test usually fails like this when runned with sanitizers:
+ *
+ * pure virtual method called
+ * terminate called without an active exception
+ * Aborted (core dumped)
+ *
+ * Disabled until we can figure out how to fix it.
  */
-TEST(async_key_value_source_test, prune_old_metadata) {
+TEST(async_key_value_source_test, DISABLED_prune_old_metadata) {
 	const uint64_t DELAY_MS = 0;
 	const uint64_t TTL_MS = 20;