Return all mappings for a timezone id in `country_zones`

Some timezones like `Europe/London` have multiple mappings in
`ActiveSupport::TimeZone::MAPPING` so return all of them instead
of the first one found by using `Hash#value`. e.g:

  # Before
  ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh"]

  # After
  ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh", "London"]

Fixes #31668.

1 files changed, 5 insertions, 2 deletions

diff --git a/activesupport/lib/active_support/values/time_zone.rb b/activesupport/lib/active_support/values/time_zone.rb
index 1de4748a46..9dfaddb825 100644
--- a/activesupport/lib/active_support/values/time_zone.rb
+++ b/activesupport/lib/active_support/values/time_zone.rb
@@ -267,11 +267,14 @@ module ActiveSupport
           country = TZInfo::Country.get(code)
           country.zone_identifiers.map do |tz_id|
             if MAPPING.value?(tz_id)
-              self[MAPPING.key(tz_id)]
+              MAPPING.inject([]) do |memo, (key, value)|
+                memo << self[key] if value == tz_id
+                memo
+              end
             else
               create(tz_id, nil, TZInfo::Timezone.new(tz_id))
             end
-          end.sort!
+          end.flatten(1).sort!
         end
 
         def zones_map