clarify error message of macros in pymethods

Co-authored-by: Bruno Kolenbrander <[email protected]>

pyo3-macros-backend/src/pyimpl.rs

@@ -151,7 +151,7 @@ pub fn impl_methods(
             }
             syn::ImplItem::Macro(m) => bail_spanned!(
                 m.span() =>
-                "macros cannot be used in `#[pymethods]` impl blocks\n\
+                "macros cannot be used as items in `#[pymethods]` impl blocks\n\
                  = note: this was previously accepted and ignored"
             ),
             _ => {}