terminalwriter: move Win32ConsoleWriter definition under win32 conditional

This way non-Windows platforms skip it. It also uses things defined
inside the `if`.

src/_pytest/_io/terminalwriter.py

@@ -300,6 +300,25 @@ class TerminalWriter:
             self.write(" " * diff2last)
 
 
+class WriteFile:
+    def __init__(self, writemethod, encoding=None):
+        self.encoding = encoding
+        self._writemethod = writemethod
+
+    def write(self, data):
+        if self.encoding:
+            data = data.encode(self.encoding, "replace")
+        self._writemethod(data)
+
+    def flush(self):
+        return
+
+
+if win32_and_ctypes:
+    import ctypes  # noqa: F811
+    from ctypes import wintypes
+    from ctypes import windll  # type: ignore[attr-defined] # noqa: F821
+
     class Win32ConsoleWriter(TerminalWriter):
         def write(self, msg, **kw):
             if msg:
@@ -333,26 +352,6 @@ class Win32ConsoleWriter(TerminalWriter):
                 if oldcolors:
                     SetConsoleTextAttribute(handle, oldcolors)
 
-
-class WriteFile:
-    def __init__(self, writemethod, encoding=None):
-        self.encoding = encoding
-        self._writemethod = writemethod
-
-    def write(self, data):
-        if self.encoding:
-            data = data.encode(self.encoding, "replace")
-        self._writemethod(data)
-
-    def flush(self):
-        return
-
-
-if win32_and_ctypes:
-    import ctypes  # noqa: F811
-    from ctypes import wintypes
-    from ctypes import windll  # type: ignore[attr-defined] # noqa: F821
-
     TerminalWriter = Win32ConsoleWriter  # type: ignore[misc] # noqa: F821
 
     # ctypes access to the Windows console