Fix sqllogictests link in contributor-guide/index.md

The crate was moved so the link needs to be updated

Author: qrilka

docs/source/contributor-guide/index.md

@@ -151,7 +151,7 @@ Tests for code in an individual module are defined in the same source file with
 
 ### sqllogictests Tests
 
-DataFusion's SQL implementation is tested using [sqllogictest](https://github.com/apache/arrow-datafusion/tree/main/datafusion/core/tests/sqllogictests) which are run like any other Rust test using `cargo test --test sqllogictests`.
+DataFusion's SQL implementation is tested using [sqllogictest](https://github.com/apache/arrow-datafusion/tree/main/datafusion/sqllogictest) which are run like any other Rust test using `cargo test --test sqllogictests`.
 
 `sqllogictests` tests may be less convenient for new contributors who are familiar with writing `.rs` tests as they require learning another tool. However, `sqllogictest` based tests are much easier to develop and maintain as they 1) do not require a slow recompile/link cycle and 2) can be automatically updated via `cargo test --test sqllogictests -- --complete`.