Fix crash caused by fail-on-violation and no lintable files in target

[tokongs]

#331 introduced a bug where the noop lint fails if running with fail on validation.

If we have a lint aspect that has no files to lint and run with fail-on-validation the exit_code file will be set to None. Which is why we need to check that its not None before trying to access its path.

Relevant error

Traceback (most recent call last):
        File "/home/tokongs/.cache/bazel/_bazel_tokongs/51d0d670cf09bb319bf1151bdc73a969/external/aspect_rules_lint~/lint/ruff.bzl", line 165, column 25, in _ruff_aspect_impl
                noop_lint_action(ctx, outputs)
        File "/home/tokongs/.cache/bazel/_bazel_tokongs/51d0d670cf09bb319bf1151bdc73a969/external/aspect_rules_lint~/lint/private/lint_aspect.bzl", line 144, column 65, in noop_lint_action
                commands.append("echo 0 > {}".format(outputs.human.exit_code.path))
Error: 'NoneType' value has no field or method 'path'

---

Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: no
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: yes

Suggested release notes: fix crash caused by noop lints running with fail-on-validation

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