Rollup merge of #128235 - harryscholes:fix-iterator-filter-docs, r=tgross35

Fix `Iterator::filter` docs

Small fix to add code formatting around `Iterator::filter` `true` return type

library/core/src/iter/traits/iterator.rs

@@ -823,7 +823,7 @@ fn call<T>(mut f: impl FnMut(T)) -> impl FnMut((), T) {
     ///
     /// Given an element the closure must return `true` or `false`. The returned
     /// iterator will yield only the elements for which the closure returns
-    /// true.
+    /// `true`.
     ///
     /// # Examples
     ///