gh-149831: Fix ctypes DLL library name on Cygwin (#149832)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: carlo-bramini

Lib/ctypes/__init__.py

@@ -549,9 +549,11 @@ def LoadLibrary(self, name):
 
 if _os.name == "nt":
     pythonapi = PyDLL("python dll", None, _sys.dllhandle)
-elif _sys.platform in ["android", "cygwin"]:
+elif _sys.platform == "android":
     # These are Unix-like platforms which use a dynamically-linked libpython.
     pythonapi = PyDLL(_sysconfig.get_config_var("LDLIBRARY"))
+elif _sys.platform == "cygwin":
+    pythonapi = PyDLL(_sysconfig.get_config_var("DLLLIBRARY"))
 else:
     pythonapi = PyDLL(None)