test: mark test_buffer/test_finalizer flaky

Refs: nodejs#43389

Mark new test as flaky as it seems to have
had intermittent failures since it was added.

Signed-off-by: Michael Dawson <[email protected]>

Author: mhdawson

test/node-api/node-api.status

@@ -5,5 +5,6 @@ prefix node-api
 # sample-test                        : PASS,FLAKY
 
 [true] # This section applies to all platforms
+test_buffer/test_finalizer : PASS,FLAKY
 
 [$system==win32]