[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.

crates/uv-static/src/env_vars.rs

@@ -87,7 +87,7 @@ impl EnvVars {
 
     /// Equivalent to the `--index-strategy` command-line argument.
     ///
-    /// For example, if set to `unsafe-any-match`, uv will consider versions of a given package
+    /// For example, if set to `unsafe-best-match`, uv will consider versions of a given package
     /// available across all index URLs, rather than limiting its search to the first index URL
     /// that contains the package.
     pub const UV_INDEX_STRATEGY: &'static str = "UV_INDEX_STRATEGY";

docs/configuration/environment.md

@@ -115,7 +115,7 @@ space-separated list of URLs as additional indexes when searching for packages.
 
 Equivalent to the `--index-strategy` command-line argument.
 
-For example, if set to `unsafe-any-match`, uv will consider versions of a given package
+For example, if set to `unsafe-best-match`, uv will consider versions of a given package
 available across all index URLs, rather than limiting its search to the first index URL
 that contains the package.