Take waitpid03 (back) out of CI. It has been flaky, and should not have gone back into CI without pretty exhaustive testing.

LibOS/shim/test/apps/ltp/FLAKY

@@ -3,7 +3,7 @@ Flaky tests
 
 These should be debugged, or revisited after memory debugging PRs are merged
 
-waitpid03,1 - fails about 20% of the time
+waitpid03,1 and 2 - fails about 20% of the time
 preadv01 - fails intermittently in CI - perhaps an unrelated bug?
 preadv01,2
 preadv01,3

LibOS/shim/test/apps/ltp/PASSED

@@ -1051,8 +1051,6 @@ waitpid01,2
 waitpid02,1
 waitpid02,2
 waitpid02,3
-waitpid03,1
-waitpid03,2
 waitpid05,1
 waitpid05,2
 waitpid05,3