amazon-ssm-agent: skip time dependent/flaky test

Build regularly fails because of time dependent tests:

* Test name: TestSendStreamDataMessageWithStreamDataSequenceNumberMutexLocked
* File: agent/session/datachannel/datachannel_test.go#L259 (refs/tags/3.2.1705.0)

This test is a time-based unit test, and relies on `time.Sleep`.
We should disable it to get the ssm build working again.

pkgs/by-name/am/amazon-ssm-agent/package.nix

@@ -131,6 +131,11 @@ buildGoModule rec {
     runHook postInstall
   '';
 
+  checkFlags = [
+    # Skip time dependent/flaky test
+    "-skip=TestSendStreamDataMessageWithStreamDataSequenceNumberMutexLocked"
+  ];
+
   postFixup = ''
     wrapProgram $out/bin/amazon-ssm-agent --prefix PATH : ${bashInteractive}/bin
   '';