fix: ignore mypy attr-defined error for SDistCommand.dry_run

Author: omry

build_helpers/build_helpers.py

@@ -147,7 +147,7 @@ def run(self) -> None:  # type: ignore
 
 class SDistCommand(sdist.sdist):  # pragma: no cover
     def run(self) -> None:
-        if not self.dry_run:
+        if not self.dry_run:  # type: ignore[attr-defined]
             self.run_command("clean")
             run_antlr(self)
         sdist.sdist.run(self)