fixup! docs: SortedSet in the changelog and the collection table

The changelog says that `SortedSet.isProperSuperset` counts the elements that the comparer of
the first set finds equal once, as the documentation of `ImmutableSortedSet.IsProperSupersetOf`
says.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: xperiandri

CHANGELOG.md

@@ -72,6 +72,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   contain strings, compare ordinally instead of in the order of the current culture.
 * `SortedSet`: `difference set1 set2` returns the elements of `set1` that are not in `set2`, as `Set.difference` does; it
   took its arguments in the reverse order before.
+* `SortedSet`: `isProperSuperset set1 set2` counts the elements of `set2` that the comparer of `set1` finds equal once, as
+  the documentation of `ImmutableSortedSet.IsProperSupersetOf` says; it counted each of them before.
 * `SortedSet`: `length` is renamed to `count` and `keyComparer` to `comparer`.
 * `SortedSet`: `filter`, `partition` and the set algebra keep the comparer of their input, the set algebra that of the
   first set. `filter` dropped the comparer before.