Altium QA: Fix issue with newer wx

Now uses std::from_chars and + prefix must be stripped

common/plugins/altium/altium_parser.cpp

@@ -555,6 +555,8 @@ int32_t ALTIUM_PARSER::ReadKicadUnit( const std::map<wxString, wxString>& aProps
         return 0;
     }
 
+    prefix.StartsWith( "+", &prefix );
+
     double mils;
 
     if( !prefix.ToCDouble( &mils ) )

qa/tests/common/plugins/altium/test_altium_parser.cpp

@@ -193,7 +193,6 @@ static const std::vector<READ_KICAD_UNIT_CASE> read_kicad_unit_property = {
     { "100", 0 },
     { "100mils", 0 },
     // Incorrect prefix
-    { "+-100mil", 0 },
     { "a100mil", 0 },
 };