MAINT: Update branch name

xref Parcels-code/Parcels#2487 (comment)

Author: VeckoTheGecko

asv.conf.json

@@ -3,7 +3,7 @@
   "project": "parcels",
   "project_url": "https://github.com/Parcels-Code/parcels",
   "repo": "https://github.com/Parcels-Code/parcels.git",
-  "branches": ["v4-dev"],
+  "branches": ["main"],
   "environment_type": "rattler",
   "conda_channels": ["conda-forge", "defaults", "https://repo.prefix.dev/parcels"],
   "default_benchmark_timeout": 1800,