fix 2 bugs: the updated max_error_weight was not tested + add->union

Author: ClementPernet

src/sage/coding/linear_code.py

@@ -4582,8 +4582,8 @@ def _build_lookup_table(self):
             self._decoder_type.add("bounded_distance")
         # Update decoder types depending on whether we are decoding beyond d/2
         if self._code_minimum_distance:
-            if t == (self._code_minimum_distance-1)//2:
-                self._decoder_type.add("minimum-distance", "always-succeed")
+            if self._maximum_error_weight == (self._code_minimum_distance-1)//2:
+                self._decoder_type.union({"minimum-distance","always-succeed"})
             else:
                 # then t > (d-1)/2
                 self._decoder_type.add("might-error")