Coverity Bug: repodlgs_common.cpp: 181 in sell_all_improvements()

[jwrober]

Describe the bug
1 new defect(s) introduced to longturn/freeciv21 found with Coverity Scan.

New defect(s) Reported-by: Coverity Scan
Showing 1 of 1 defect(s)

** CID 1587153: Performance inefficiencies (COPY_INSTEAD_OF_MOVE)
/client/repodlgs_common.cpp: 181 in sell_all_improvements(const impr_type *, bool, char *, unsigned long)()

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*** CID 1587153:  Performance inefficiencies  (COPY_INSTEAD_OF_MOVE)
/client/repodlgs_common.cpp: 181 in sell_all_improvements(const impr_type *, bool, char *, unsigned long)()
175       city_list_iterate(client.conn.playing->cities, pcity)
176       {
177         cities.append(pcity);
178       }
179       city_list_iterate_end;
180     
>>>     CID 1587153:  Performance inefficiencies  (COPY_INSTEAD_OF_MOVE)
>>>     "cities" is passed-by-value as parameter to "sell_all_improvements_for_cities" when it could be moved instead.
181       sell_all_improvements_for_cities(cities, pimprove, redundant_only, message,
182                                        message_sz);
183     }
184     
185     /**
186        Sell all improvements of the given type in cities.  If

Additional context
Seems to be from this recent change: #2484