Remove Symbol/str mypy suppression (#9472)

Author: JosueNina

run_syntax_check.py

@@ -72,7 +72,6 @@ def should_ignore(line: str, prev_line_ignored: bool) -> bool:
         'Too many arguments for "update" of "IndicatorBase"',
         'Signature of "update" incompatible with supertype "IndicatorBase"',
         'Signature of "update" incompatible with supertype "QuantConnect.Indicators.IndicatorBase"',
-        'has incompatible type "Symbol"; expected "str"',
         # This methods take an indicator and consolidator which might be instances of custom
         # indicator/consolidator Python classes that don't inherit from PythonIndicator or IDataConsolidator
         'No overload variant of "register_indicator" of "QCAlgorithm" matches argument types',