test: mark tests as flaky as intermediate step

We have a few http2 issues that are currently resolved. Until they
are, just mark these two tests as flaky.

PR-URL: #20835
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

test/parallel/parallel.status

@@ -8,6 +8,12 @@ prefix parallel
 # Postmortem debugging data is prone to accidental removal during V8 updates.
 test-postmortem-metadata: PASS,FLAKY
 
+# http2 has a few bugs that make these tests flaky and that are currently worked
+# on.
+test-http2-client-upload-reject: PASS,FLAKY
+test-http2-pipe: PASS,FLAKY
+test-http2-client-upload: PASS,FLAKY
+
 [$system==win32]
 
 [$system==linux]