[3.12] Replace the term `Immutable` with a `Hashable` in the `sequence` entry of the Glossary (GH-124350) (#124353)

Replace the term `Immutable` with a `Hashable` in the `sequence` entry of the Glossary (GH-124350)

The term `Immutable` in the `sequence` entry of the glossary is used incorrectly, in fact dicts accepts hashable keys, which is not the same as immutable.
(cherry picked from commit 6203ef35dd4ee9dd59759ce83eace8eacac69685)

Co-authored-by: decorator-factory <42166884+decorator-factory@users.noreply.github.com>