feat(tests): mirror mysql84-g[1-5] test sets into mysql95-g[1-5]

Every TAP test currently executed against mysql84-g[1-5] is now also
executed against the corresponding mysql95-g[1-5] group. Same 5-bucket
split, same assignment per bucket:

  mysql84-g1: 78  →  mysql95-g1: 78
  mysql84-g2: 42  →  mysql95-g2: 42
  mysql84-g3: 40  →  mysql95-g3: 40
  mysql84-g4: 60  →  mysql95-g4: 60
  mysql84-g5:  5  →  mysql95-g5:  5
  total:     225      total:    225

Rationale: validates the full 8.4 test surface on MySQL 9.5, which is
the whole point of adding the 9.x infras — different MySQL major
versions catch different regressions (e.g., mysql_native_password
removal in 9.0). Group Replication variants (mysql*-gr-g*) are
intentionally out of scope for now.

Scripted via a simple walk over groups.json: for each entry containing
mysql84-gN, add mysql95-gN if missing, then re-sort. Verified:
  - 209 new memberships added (225 target - 16 already existing from
    the earlier mysql95-g1 seeding)
  - check_groups.py reports 385/385 tests registered, no orphans
  - per-bucket counts now match mysql84-g[1-5] exactly

Author: renecannao