tests: add more merge+successors cases for stack

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branch : stable
8 jobs for topic/stable/stack-bugs in 4 minutes and 6 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed checks-py2 #126907

00:02:54

passed checks-py3 #126908

00:00:59

passed doc #126913

00:00:29

manual pytype #126906
allowed to fail manual
passed tests-py2-cext #126909

00:03:13

passed tests-py2-pure #126910

00:04:06

passed tests-py3-cext #126911

00:03:18

passed tests-py3-pure #126912

00:03:48