Fix typo in MissingTopLevel warning (#16351)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
The warning shown when `egg-info` lacks `top_level.txt` incorrectly
warns about missing `top-level.txt`
https://github.com/astral-sh/uv/blob/ee2649feaa78b847ebcd44daebdce28c2e974842/crates/uv-install-wheel/src/uninstall.rs#L179-L188
https://github.com/astral-sh/uv/blob/ee2649feaa78b847ebcd44daebdce28c2e974842/crates/uv/src/commands/pip/operations.rs#L687-L693
The non fatal warning with incorrect filename was introduced in
https://github.com/astral-sh/uv/pull/6881 which changed previous fatal
error https://github.com/astral-sh/uv/issues/6872 with correct
`top_level.txt` output.
## Test Plan
<!-- How was it tested? -->
Updated unit test to reflect change in warning
