Update petab/v2/petab1to2.py

Co-authored-by: Dilan Pathirana <59329744+dilpath@users.noreply.github.com>

Author: dweindl

petab/v2/petab1to2.py

@@ -106,7 +106,7 @@ def create_experiment_id(sim_cond_id: str, preeq_cond_id: str) -> str:
                 return ""
             if preeq_cond_id:
                 preeq_cond_id = f"{preeq_cond_id}_"
-            exp_id = f"experiment_{preeq_cond_id}{sim_cond_id}"
+            exp_id = f"experiment__{preeq_cond_id}__{sim_cond_id}"
             if exp_id in experiments:  # noqa: B023
                 i = 1
                 while f"{exp_id}_{i}" in experiments:  # noqa: B023