Don't use is comparisons for sympy objects (#3026)

`is` comparisons for `sympy.Symbol` or other sympy expressions are fragile and shouldn't be relied on.

Author: dweindl

python/sdist/amici/importers/sbml/__init__.py

@@ -2714,7 +2714,7 @@ def _clean_reserved_symbols(self) -> None:
                 if old_symbol in symbols:
                     # reconstitute the whole dict in order to keep the ordering
                     self.symbols[symbols_ids] = {
-                        new_symbol if k is old_symbol else k: v
+                        new_symbol if k == old_symbol else k: v
                         for k, v in symbols.items()
                     }