sort autofix incorrectly removes nested sorts

[BorisOrca]

Minimal reproduction:

values = [(2, "b"), (2, "a"), (1, "b"), (1, "a")]
print(sorted(sorted(values, key=lambda x: x[1]), key=lambda x: x[0]))

prints out: [(1, 'a'), (1, 'b'), (2, 'a'), (2, 'b')]

After running ruff check reproduce_sort_issue.py
Found 1 error (1 fixed, 0 remaining).

The "fixed" code is:

values = [(2, "b"), (2, "a"), (1, "b"), (1, "a")]
print(sorted(values, key=lambda x: x[0]))

prints out: [(1, 'b'), (1, 'a'), (2, 'b'), (2, 'a')]

> ruff --version
ruff 0.0.277

[charliermarsh]

Looks like we need to avoid collapsing sorts with different keys.