add symlink to python3 in modal runner

Author: Mark Saroufim

src/runners/modal_runner.py

@@ -17,6 +17,7 @@
 # Move this to another file later:
 cuda_image = (
     Image.from_registry(f"nvidia/cuda:{tag}", add_python="3.13")
+    .run_commands("ln -sf $(which python) /usr/local/bin/python3")
     .apt_install(
         "git",
         "gcc-13",