fix: version logic

[Florian Ruppel (fruppel)]

Latest tag is e.g. v6.7.10.0.

• 6.7.11.x branch doesn't exist → 6.7.11.0 is still open for development → NEXT_MINOR=6.7.11.0
• 6.7.11.x branch exists → 6.7.11.0 is frozen for release → trunk PRs should target the version after → NEXT_MINOR=6.7.12.0

[Florian Ruppel (fruppel)]

$ ./print_versions.bash
PREV_MAJOR_MIN_TAG=v6.6.0.0
PREV_MAJOR_MAX_TAG=v6.6.10.18
CUR_MAJOR_MIN_TAG=v6.7.0.0
CUR_MAJOR_MAX_TAG=v6.7.10.2
NEXT_MINOR=v6.7.12.0
NEXT_PATCH=v6.7.10.3
NEXT_LTS_PATCH=v6.6.10.19