feat: variables start with a _ are no longer beeing reported as unused

closes #258

Author: d-biehl

packages/language_server/src/robotcode/language_server/robotframework/parts/diagnostics.py

@@ -395,6 +395,9 @@ def _collect_unused_variable_references(self, document: TextDocument) -> Diagnos
                 ):
                     continue
 
+                if var.name_token is not None and var.name_token.value and var.name_token.value.startswith("_"):
+                    continue
+
                 references = self.parent.robot_references.find_variable_references(document, var, False, True)
                 if not references:
                     result.append(