fix: use sys.executable instead of hardcoded "python" in tests

Tests that launch the API server via subprocess used a hardcoded
"python" command which fails on systems where only "python3" is
available (e.g. macOS). Using sys.executable ensures the same
interpreter running pytest is used for subprocesses.

Fixes 36 test errors on macOS environments.

atroposlib/tests/api_test_utils.py

@@ -1,4 +1,5 @@
 import subprocess
+import sys
 import time
 
 import requests
@@ -16,7 +17,7 @@ def launch_api_for_testing(max_wait_for_api: int = 10) -> subprocess.Popen:
     # Use subprocess instead of multiprocessing to avoid inheriting pytest args
     api_proc = subprocess.Popen(
         [
-            "python",
+            sys.executable,
             "-m",
             "atroposlib.cli.run_api",
             "--host",