sdf: use an explicit static function to select the appropriate versio…

…n of SdfPredicateExpression::GetParseError() to use in Python wrapping

When building using C++20, Boost seems to be unable to correctly deduce which
version of GetParseError() to use when wrapping to Python. This change adds a
static function that ensures the version returning a const reference is used,
which was the original intent.

pxr/usd/sdf/wrapPredicateExpression.cpp

@@ -50,7 +50,12 @@ _Repr(SdfPredicateExpression const &self) {
             + TfPyRepr(self.GetText()) + ")";
     }
 }
-
+
+static std::string const&
+_GetParseError(SdfPredicateExpression const &self) {
+    return self.GetParseError();
+}
+
 void wrapPredicateExpression()
 {
     TfPyFunctionFromPython<void (PredExpr::Op, int)> {};
@@ -96,9 +101,7 @@ void wrapPredicateExpression()
         .def(self == self)
         .def(self != self)
 
-        .def("GetParseError",
-             static_cast<std::string const &(PredExpr::*)() const &>(
-                 &PredExpr::GetParseError),
+        .def("GetParseError", &_GetParseError,
              return_value_policy<return_by_value>())
         ;