[skip ci] Bring CHANGELOG up to date

Unreleased

Drop support for Rails 5.2 and 6.0 as well as Ruby 2.6 and 2.7 they've been end-of-lifed by @dougmrqs and @HeitorMC. The gem now supports Ruby 3.0+ and Rails 6.1+. (#1521, #1522, #1547, #1548)

Fix validate_uniqueness_of matcher not supporting column of the type timestampz by @callahat. (#1544)
Ensure that validation specs work for ActiveModel without ActiveRecord by @stonefield. (#1580)

Add normalize matcher by @stephannv. (#1558)
Add support for Ruby 3.2 by @petergoldstein. (#1536)
Add support for Ruby 3.3.0-rc1 by @mtasaka and @VSPPedro. (#1579, #1588)
Add support for Rails 7.1 by @matsales28. (#1573)
Add support for array attributes on validate_length_of matcher by @jarenas9539. #1560
Allow length validation on associations by @matsales28. (#1569)
Improve have_db_index to better handle columns with multiple indexes by @abrom. (#1542)
Implement of_sql_type qualifier on have_db_column matcher by @matsales28. (#1555)

When an unrelated error is seen with negated allow_value, give a hint by @matsales28. (#1570)