fix: run validation pipelines using latest clas12Tags semver tag

[c-dilks]

Better fix for #168 (supersedes #169)

Triggers clas12-validation workflow run using the highest semantically-versioned tag from clas12Tags.

• highest semantic version is preferred over latest tag, since there may be backports to older tags which occur in the git DAG later than semantically later tags
• assumes that tag is working
• ignores the dev tag, which appears to be moving; it's ignored because it is not a semantic version number
• this automation is a better approach than choosing a fixed tag, since we may eventually forget to increment it