Fixes #1898: Windows guard in is_available() compares os.system (a function) to 'nt' — always False

- Changed `os.system == 'nt'` to `sys.platform == 'win32'` 
- This fixes the Windows detection logic that was previously broken
- The function now properly short-circuits on Windows systems

Author: vinayK34

httpie/output/ui/man_pages.py

@@ -2,12 +2,14 @@
 
 import subprocess
 import os
+import sys
 from httpie.context import Environment
 
 
 MAN_COMMAND = 'man'
 NO_MAN_PAGES = os.getenv('HTTPIE_NO_MAN_PAGES', False)
 
+
 # On some systems, HTTP(n) might exist, but we are only interested in HTTP(1).
 # For more information on man page sections: <https://unix.stackexchange.com/a/138643>
 MAN_PAGE_SECTION = '1'
@@ -18,7 +20,7 @@ def is_available(program: str) -> bool:
     Check whether `program`'s man pages are available on this system.
 
     """
-    if NO_MAN_PAGES or os.system == 'nt':
+    if NO_MAN_PAGES or sys.platform == 'win32':
         return False
     try:
         process = subprocess.run(
@@ -45,4 +47,4 @@ def display_for(env: Environment, program: str) -> None:
         [MAN_COMMAND, MAN_PAGE_SECTION, program],
         stdout=env.stdout,
         stderr=env.stderr
-    )
+    )