Silence Coverity warning

Not an issue since the caller is synchronized but protect access to the
transactionRegistry for consistency.

Author: markt-asf

java/org/apache/tomcat/dbcp/dbcp2/managed/BasicManagedDataSource.java

@@ -108,7 +108,7 @@ protected synchronized ConnectionFactory createConnectionFactory() throws SQLExc
     }
 
     @Override
-    protected DataSource createDataSourceInstance() throws SQLException {
+    protected synchronized DataSource createDataSourceInstance() throws SQLException {
         final PoolingDataSource<PoolableConnection> pds = new ManagedDataSource<>(getConnectionPool(),
                 transactionRegistry);
         pds.setAccessToUnderlyingConnectionAllowed(isAccessToUnderlyingConnectionAllowed());