It must have been during the Soviet rule.
If any name-changing happened after 1991, it's changing Soviet names back to their pre-revolutionary name.
A part of the name-changing happened during the 1920's but I haven't found anything about this particular street.
But seeing as Liebknecht was a communist revolutionary in Germany who was tortured, interrogated and then shot in 1919, I wouldn't be surprised if that street was named after him not long after his death.