Add caveat to popen_with_stderr #734

Job	Run time
check-skip	1s
Build Apache Cloudberry	9m 44s
prepare-test-matrix	1s
RPM Install Test Apache Cloudberry	38s
ic-good-opt-off	26m 15s
ic-good-opt-on	30m 22s
ic-expandshrink	2m 50s
ic-singlenode	6m 49s
ic-resgroup-v2	18m 22s
ic-contrib	2m 32s
ic-gpcontrib	2m 43s
ic-fixme	2m 8s
ic-isolation2	24m 28s
ic-isolation2-crash	3m 5s
ic-parallel-retrieve-cursor	2m 47s
Generate Apache Cloudberry Build Report	1s
	2h 12m 46s

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