[shared_preferences] Fix typo in changelog (#7523)

This PR fixes a typo in the changelog of shared_preferences, relating to what Dart / Flutter version are supported from version 2.3.2 onwards

Fixes flutter/flutter#154177

I'm not sure if this requires a version change. Does it fall under "Updating the minimum Dart or Flutter SDK for all packages when we adjust our test matrix." ? Although, developers probably want to see this corrected on Pub, so that would require a version change?

packages/shared_preferences/shared_preferences/CHANGELOG.md

@@ -2,7 +2,6 @@
 
 * Removes outdated testing information from README.
 * Updates minimum supported SDK version to Flutter 3.22/Dart 3.4.
-* Updates minimum supported SDK version to Flutter 3.19/Dart 3.3.
 
 ## 2.3.1