Backport ci deb: tweak downgrade test case #3103

Job	Run time
Build (Debian bullseye amd64)	13m 1s
Build (Debian bookworm amd64)	13m 15s
Build (Ubuntu Focal amd64)	14m 11s
Build (Ubuntu Jammy amd64)	31m 34s
Build (Ubuntu Noble amd64)	26m 47s
Test Debian bullseye amd64 update-from-v4.sh	58s
Test Debian bullseye amd64 update-to-next-version-with-backward-compat-for-v4.sh	1m 14s
Test Debian bullseye amd64 downgrade-to-v4.sh	1m 9s
Test Debian bullseye amd64 install-newly.sh local	57s
Test Debian bullseye amd64 install-newly.sh v5	55s
Test Debian bullseye amd64 install-newly.sh lts	55s
Test Debian bookworm amd64 install-newly.sh local	55s
Test Debian bookworm amd64 install-newly.sh v5	1m 10s
Test Debian bookworm amd64 install-newly.sh lts	1m 0s
Test Ubuntu Focal amd64 update-from-v4.sh	1m 49s
Test Ubuntu Focal amd64 update-to-next-version-with-backward-compat-for-v4.sh	2m 7s
Test Ubuntu Focal amd64 downgrade-to-v4.sh	1m 47s
Test Ubuntu Focal amd64 install-newly.sh local	1m 25s
Test Ubuntu Focal amd64 install-newly.sh v5	1m 43s
Test Ubuntu Focal amd64 install-newly.sh lts	1m 31s
Test Ubuntu Jammy amd64 update-from-v4.sh	1m 35s
Test Ubuntu Jammy amd64 update-to-next-version-with-backward-compat-for-v4.sh	2m 27s
Test Ubuntu Jammy amd64 downgrade-to-v4.sh	1m 50s
Test Ubuntu Jammy amd64 install-newly.sh local	1m 45s
Test Ubuntu Jammy amd64 install-newly.sh v5	1m 33s
Test Ubuntu Jammy amd64 install-newly.sh lts	1m 52s
Test Ubuntu Noble amd64 install-newly.sh local	1m 15s
	2h 10m 40s

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