Fix the worker for Windows

This disables --beat on Windows and sets FORKED_BY_MULTIPROCESSING=1, which is
required to make the default celery pool work on Windows.

conda-store-server/conda_store_server/worker/app.py

@@ -71,9 +71,18 @@ def start(self):
         argv = [
             "worker",
             "--loglevel=INFO",
-            "--beat",
         ]
 
+        # The default Celery pool requires this on Windows. See
+        # https://stackoverflow.com/questions/37255548/how-to-run-celery-on-windows
+        if sys.platform == "win32":
+            os.environ.setdefault('FORKED_BY_MULTIPROCESSING', '1')
+        else:
+            # --beat does not work on Windows
+            argv += [
+                "--beat",
+            ]
+
         if self.concurrency:
             argv.append(f"--concurrency={self.concurrency}")