gioerror: Map ETXTBSY to G_FILE_ERROR_BUSY

It's a busy text file, but we don't care much about specifics so we
can just return the generic busy error.

(cherry-picked from commit 6bc6b7ef30)

gio/gioerror.c

@@ -217,6 +217,12 @@ g_io_error_from_errno (gint err_no)
       break;
 #endif
 
+#ifdef ETXTBSY
+    case ETXTBSY:
+      return G_IO_ERROR_BUSY;
+      break;
+#endif
+
 #ifdef EWOULDBLOCK
     case EWOULDBLOCK:
       return G_IO_ERROR_WOULD_BLOCK;