What are these two Sewer Pipes Coming up Out the Ground?
They are probably additional clean-out-points - my local inspector wants one every 50 feet (15 meters) along the line. But my comment that you should ask the people who put them in, who would know, stands as the correct way to figure that out.

If so, they should remain accessible, but be protected from sunlight, as they appear to be PVC. You can paint them for basic sun protection, or my preferred approach is to build a small rock or brick wall around and put a large flat rock or patio block on top of it - easy to find, easy to access, but out of sight and out of sunlight.

Should not affect your planned garden particularly, though you should beware of the possibility that they MAY not be vertical all the way to the buried line - they might angle towards the street before the connection to the line, so when digging near them, dig slowly and carefully. Non-perforated PVC pipes are far less "root infiltratable" than clay pipes were.