[libc++][NFC] Replace tab with whitespace in comment

There is a stray tab character in a comment block. Replace the tab
character with a space for consistency with other comments.

NOKEYCHECK=True
GitOrigin-RevId: 67964fc4b241ef02705c44ff5d58e61e5bf8b38f
diff --git a/include/filesystem b/include/filesystem
index 108fadd..ccb7bc4 100644
--- a/include/filesystem
+++ b/include/filesystem
@@ -277,7 +277,7 @@
   uintmax_t available;
 };
 
-// On Windows, the library never identifies files as  block, character, fifo
+// On Windows, the library never identifies files as block, character, fifo
 // or socket.
 enum class _LIBCPP_ENUM_VIS file_type : signed char {
   none = 0,