Add warning about run/import Airflow under the Windows (#39196)

airflow/__init__.py

@@ -21,6 +21,7 @@
 
 import os
 import sys
+import warnings
 
 if os.environ.get("_AIRFLOW_PATCH_GEVENT"):
     # If you are using gevents and start airflow webserver, you might want to run gevent monkeypatching
@@ -30,6 +31,17 @@
 
     patch_all()
 
+if sys.platform == "win32":
+    warnings.warn(
+        "Airflow currently can be run on POSIX-compliant Operating Systems. For development, "
+        "it is regularly tested on fairly modern Linux Distros and recent versions of macOS. "
+        "On Windows you can run it via WSL2 (Windows Subsystem for Linux 2) or via Linux Containers. "
+        "The work to add Windows support is tracked via https://github.com/apache/airflow/issues/10388, "
+        "but it is not a high priority.",
+        category=RuntimeWarning,
+        stacklevel=1,
+    )
+
 # The configuration module initializes and validates the conf object as a side effect the first
 # time it is imported. If it is not imported before importing the settings module, the conf
 # object will then be initted/validated as a side effect of it being imported in settings,
@@ -76,8 +88,6 @@ def __getattr__(name: str):
     module_path, attr_name, deprecated = __lazy_imports.get(name, ("", "", False))
     if not module_path:
         if name.startswith("PY3") and (py_minor := name[3:]) in ("6", "7", "8", "9", "10", "11", "12"):
-            import warnings
-
             warnings.warn(
                 f"Python version constraint {name!r} is deprecated and will be removed in the future. "
                 f"Please get version info from the 'sys.version_info'.",
@@ -88,8 +98,6 @@ def __getattr__(name: str):
 
         raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
     elif deprecated:
-        import warnings
-
         warnings.warn(
             f"Import {name!r} directly from the airflow module is deprecated and "
             f"will be removed in the future. Please import it from 'airflow{module_path}.{attr_name}'.",