fix: another broken intra-doc link uncovered by --document-private-items

CI runs `cargo doc --document-private-items` which catches links on
private items (the previous fix only covered public items). The
`row_groups_pruned_dynamic` field's doc comment referenced
`[\`row_group_pruner\`]` — same-struct field, needs `Self::` to resolve.

Author: zhuqi-lucas

datafusion/datasource-parquet/src/push_decoder.rs

@@ -249,7 +249,7 @@ pub(crate) struct PushDecoderStreamState {
     /// contribute to the result. `None` when the scan has no dynamic
     /// predicate or only one decoder run.
     pub(crate) row_group_pruner: Option<RowGroupPruner>,
-    /// Count of row groups skipped at runtime by [`row_group_pruner`].
+    /// Count of row groups skipped at runtime by [`Self::row_group_pruner`].
     pub(crate) row_groups_pruned_dynamic: Count,
 }