Auto-detected project name is malformed when the program is in a sibling directory of the git repo

Bug description

wandb.util.auto_project_name() is used by wandb.init() and the CLI to pick a project name from the enclosing git repository: <repo> for a program at the repo root, <repo>-<subdir> for a program in a subdirectory.

The check that decides whether the program lives inside the repository is a plain string prefix test:

# wandb/util.py
prog_dir = os.path.dirname(os.path.abspath(program))
if not prog_dir.startswith(root_dir):
    return str(repo_name)

A sibling directory whose name shares a string prefix with the repo directory satisfies startswith even though it is not inside the repo. The generated project name then embeds a ../ relative path.

Reproduction

import os, subprocess, tempfile
import wandb.util

with tempfile.TemporaryDirectory() as td:
    repo = os.path.join(td, "repo")
    sibling = os.path.join(td, "repo2")   # shares the "repo" prefix
    os.makedirs(os.path.join(repo, "pkg"))
    os.makedirs(sibling)
    subprocess.run(["git", "init"], cwd=repo, check=True)
    os.chdir(repo)

    print(wandb.util.auto_project_name(os.path.join(repo, "pkg", "train.py")))  # repo-pkg
    print(wandb.util.auto_project_name(os.path.join(sibling, "train.py")))      # repo-.._repo2  (!)

The second call should return "repo" (the program is outside the repository), but returns "repo-.._repo2".

Expected behavior

Programs outside the repository — including sibling directories that share a name prefix — should yield the bare repo name, not a name containing ...

Environment

• wandb: current main (commit 955991a)
• Python 3.12, Linux