[docs] Fix suggestion for index strategy (#12634)
## Summary
Fix a suggestion in the docs on configs through environment variables,
which lists an option value that doesn't appear to exist.
The description implies that `unsafe-best-match` was intended here.
## Test Plan
Verified by providing `unsafe-any-match` as a parameter to `uv`. It
didn't error, but appeared to use the `first-index` strategy instead.
The value I changed it to behaves as described by the documentation.
