Improve scoping control of connetion members.

(The real bug here is that CONNECTION_GRAPH::assignNetCodesToBus() was
growing the bus aliases members list because it used a non-const
reference to it as a local storage list.  The const scoping of it will
prevent this type of error in future.)

Fixes https://gitlab.com/kicad/code/kicad/issues/14269

eeschema/connection_graph.cpp

@@ -1770,7 +1770,7 @@ int CONNECTION_GRAPH::assignNewNetCode( SCH_CONNECTION& aConnection )
 
 void CONNECTION_GRAPH::assignNetCodesToBus( SCH_CONNECTION* aConnection )
 {
-    std::vector< std::shared_ptr<SCH_CONNECTION>>& connections_to_check( aConnection->Members() );
+    std::vector<std::shared_ptr<SCH_CONNECTION>> connections_to_check( aConnection->Members() );
 
     for( unsigned i = 0; i < connections_to_check.size(); i++ )
     {

eeschema/sch_connection.h

@@ -185,11 +185,6 @@ public:
 
     wxString VectorPrefix() const { return m_vector_prefix; }
 
-    std::vector< std::shared_ptr< SCH_CONNECTION > >& Members()
-    {
-        return m_members;
-    }
-
     const std::vector< std::shared_ptr< SCH_CONNECTION > >& Members() const
     {
         return m_members;

eeschema/sch_line.cpp

@@ -903,7 +903,7 @@ void SCH_LINE::Plot( PLOTTER* aPlotter, bool aBackground ) const
     {
         if( SCH_CONNECTION* connection = Connection() )
         {
-            for( std::shared_ptr<SCH_CONNECTION>& member : connection->Members() )
+            for( const std::shared_ptr<SCH_CONNECTION>& member : connection->Members() )
                 properties.emplace_back( wxT( "!" ) + member->Name() );
         }