[release-1.5] apply scripts use wrong branch for sylva-core tags

Example provided by @ader1990 on Slack:

🔎 Validate sylva-units values for management cluster
[INFO] Using 4a052d22232481404e0e0f8783f5639130f5c805
[INFO] detected branch 3416-backport-1-5-doc-have-units-description-md-include-appversion-for-helm-charts

🔎 Validate sylva-units values for management cluster
[INFO] Using 4a052d22232481404e0e0f8783f5639130f5c805
[INFO] detected branch backport_remove_okd_1.5

The release-1.5 branch is missing fixes that landed in main and release-1.6, with the result of possibly picking a dev-branch among all the branches that contain the commit for a 1.5.x tag.