[CI] Review setup of scheduled sanitizer tests

The scheduled (LTV) sanitizer tests use the same naming convention with -enc/-dec as the check-be jobs in the MR pipelines, but the mechanism is not actually applied in the CI code, so all of the jobs do run fx enc -> fx dec.

Possible options:

• rework to have the actual enc/dec split
  • possible variant: do the rework + add three fx fullchain jobs
• keep as is and
  • remove half of the jobs to save runner resources and only keep the -dec variants because the have a larger set of testcases
  • keep exactly as is now (this may bring a tiny bit of more coverage because the -enc jobs use a different .prm file)