Fix minor bug: pcbnew file save: dimensions timestamp updated on every save

Fixes: lp:1733872
https://bugs.launchpad.net/kicad/+bug/1733872

pcbnew/pcb_parser.cpp

@@ -1624,7 +1624,11 @@ DIMENSION* PCB_PARSER::parseDIMENSION()
         case T_gr_text:
         {
             TEXTE_PCB* text = parseTEXTE_PCB();
+            // This copy  (using the copy constructor) rebuild the text timestamp,
+            // that is not what we want.
             dimension->Text() = *text;
+            // reinitialises the text time stamp to the right value (the dimension time stamp)
+            dimension->Text().SetTimeStamp( dimension->GetTimeStamp() );
             dimension->SetPosition( text->GetTextPos() );
             delete text;
             break;