gh-86009: Fix solaris detection in _USE_CP_SENDFILE check (GH-124289)

Author: kulikjak

Lib/shutil.py

@@ -48,7 +48,7 @@
 # This should never be removed, see rationale in:
 # https://bugs.python.org/issue43743#msg393429
 _USE_CP_SENDFILE = (hasattr(os, "sendfile")
-                    and sys.platform.startswith(("linux", "android", "solaris")))
+                    and sys.platform.startswith(("linux", "android", "sunos")))
 _HAS_FCOPYFILE = posix and hasattr(posix, "_fcopyfile")  # macOS
 
 # CMD defaults in Windows 10