Improve readability of UserMailer#unlock_time

This matches the new content design.

app/mailers/user_mailer.rb

@@ -115,7 +115,11 @@ def locked_time
   end
 
   def unlock_time
-    (@user.locked_at + 1.hour).to_fs(:govuk_date)
+    t = (@user.locked_at + 1.hour)
+    time_part = t.to_fs(:govuk_time)
+    date_part = t.to_date.to_fs(:govuk_date)
+
+    "#{time_part} UK time on #{date_part}"
   end
 
   def account_name

test/models/user_mailer_test.rb

@@ -156,7 +156,7 @@ def assert_support_present_in_text(link_text, email = @email)
     setup do
       GovukEnvironment.stubs(:production?).returns(false)
       GovukEnvironment.stubs(:name).returns("test")
-      @the_time = Time.zone.now
+      @the_time = Time.zone.local(2023, 10, 31, 2, 0, 0)
       user = User.new(name: "User", email: "user@example.com", locked_at: @the_time)
       @email = UserMailer.unlock_instructions(user, "afaketoken")
     end
@@ -167,7 +167,7 @@ def assert_support_present_in_text(link_text, email = @email)
     end
 
     should "state when the account will be unlocked" do
-      assert_body_includes "Your account will be unlocked at #{(@the_time + 1.hour).to_fs(:govuk_date)}"
+      assert_body_includes "Your account will be unlocked at 3:00am UK time on 31 October 2023"
     end
   end