Fix mypy warning

Author: elopez

crytic_compile/platform/etherscan.py

@@ -376,13 +376,15 @@ def compile(self, crytic_compile: "CryticCompile", **kwargs: str) -> None:
         try:
             # etherscan might return an object with two curly braces, {{ content }}
             dict_source_code = json.loads(source_code[1:-1])
+            assert isinstance(dict_source_code, dict)
             filenames, working_dir, remappings = _handle_multiple_files(
                 dict_source_code, addr, prefix, contract_name, export_dir
             )
         except JSONDecodeError:
             try:
                 # or etherscan might return an object with single curly braces, { content }
                 dict_source_code = json.loads(source_code)
+                assert isinstance(dict_source_code, dict)
                 filenames, working_dir, remappings = _handle_multiple_files(
                     dict_source_code, addr, prefix, contract_name, export_dir
                 )