Psalms 120 through 134 each carry what heading?

Answer: A song of ascents

Each of the fifteen psalms from 120 to 134 is titled "A song of ascents."

“A song of ascents. In my distress I cried to the LORD, and He answered me. A song of ascents. Come, bless the LORD, all you servants of the LORD who serve by night in the house of the LORD!”— Psalm 120:1, 134:1 (BSB)