correct handling of invalid variables in variables section

Author: d-biehl

robotcode/language_server/robotframework/diagnostics/namespace.py

@@ -93,10 +93,12 @@ async def visit_Section(self, node: ast.AST) -> None:  # noqa: N802
     async def visit_Variable(self, node: ast.AST) -> None:  # noqa: N802
         from robot.parsing.lexer.tokens import Token
         from robot.parsing.model.statements import Variable
+        from robot.variables import is_variable
 
         n = cast(Variable, node)
         name = n.get_token(Token.VARIABLE)
-        if name is not None:
+
+        if name is not None and is_variable(name.value):
             self._results.append(
                 VariableDefinition(
                     name=n.name,