gh-139322: Create test_os package

* Move test_posix.py and test_os.py to Lib/test/test_os/
* Split Windows specific test cases to a new test_windows.py file.

Author: vstinner

Lib/test/libregrtest/findtests.py

@@ -25,10 +25,11 @@
     "test_gdb",
     "test_inspect",
     "test_io",
-    "test_pydoc",
     "test_multiprocessing_fork",
     "test_multiprocessing_forkserver",
     "test_multiprocessing_spawn",
+    "test_os",
+    "test_pydoc",
 }
 
 

Lib/test/test_os/__init__.py

@@ -0,0 +1,6 @@
+import os.path
+from test.support import load_package_tests
+
+
+def load_tests(*args):
+    return load_package_tests(os.path.dirname(__file__), *args)