[Data] Normalize all dates in releases.yml to Date instead of String

[epistrephein]

In _data/releases.yml, 3 of the total 222 dates under the date: key are represented with quotes instead of without.

This has the side effect that when the file is YAML-parsed, these dates are parsed as Strings instead of Dates, creating an unwanted inconsistency of classes.

This PR normalizes the 3 dates removing the quotes so that they're all parsed as Date class.

require 'yaml'
yaml = YAML.unsafe_load_file('_data/releases.yml')

# master
yaml.filter_map { |i| i['version'] unless i['date'].is_a?(Date) }
# => ["3.3.8", "3.2.8", "3.1.7"]
yaml.find { |i| i['version'] == '3.2.8' }['date']
# => "2025-03-26"


# this branch
yaml.filter_map { |i| i['version'] unless i['date'].is_a?(Date) }
# => []
yaml.find { |i| i['version'] == '3.2.8' }['date']
# => #<Date: 2025-03-26 ((2460761j,0s,0n),+0s,-Infj)>

(see #3375 and #3146 for a similar fix some time ago)