Improve Indico extractor

This allows to differentiate the e.g. the Akademy 2021 and QtCS 2021
booking, which only differ in the subtitle.
2 jobs for release/21.08 in 10 minutes and 4 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #117790

00:09:46

passed reuse #117789
reuse

00:00:18