fix: disable airflow multiprocessing (#3097)

Author: tobymao

sqlmesh/core/constants.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import datetime
+import multiprocessing as mp
 import os
 import typing as t
 from pathlib import Path
@@ -35,7 +36,7 @@
 # None means default to process pool, 1 means don't fork, :N is number of processes
 # Factors in the number of available CPUs even if the process is bound to a subset of them
 # (e.g. via taskset) to avoid oversubscribing the system and causing kill signals
-if hasattr(os, "fork"):
+if hasattr(os, "fork") and not mp.current_process().daemon:
     try:
         MAX_FORK_WORKERS: t.Optional[int] = int(os.getenv("MAX_FORK_WORKERS"))  # type: ignore
     except TypeError: