RUBY-3571 Add TransientTransactionError label to PoolClearedError

lib/mongo/error/pool_cleared_error.rb

@@ -31,6 +31,7 @@ class PoolClearedError < PoolError
       #
       # @api private
       def initialize(address, pool)
+        add_label('TransientTransactionError')
         super(address, pool,
           "Connection to #{address} interrupted due to server monitor timeout " +
             "(for pool 0x#{pool.object_id})")

spec/mongo/error/pool_cleared_error_spec.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+require 'lite_spec_helper'
+
+describe Mongo::Error::PoolClearedError do
+  describe '#initialize' do
+    let(:error) do
+      described_class.new(double('address'), double('pool'))
+    end
+
+    it 'appends TransientTransactionError' do
+      expect(error.labels).to include('TransientTransactionError')
+    end
+  end
+end