Don't show CRLF tests as modified in the working directory

This was being overriden by `lf=eof` in `.gitattributes` in the root
directory. Override it again to avoid warnings like this:

```
$ git diff src/tools/rustfmt/tests/target/issue-3494/crlf.rs
warning: CRLF will be replaced by LF in src/tools/rustfmt/tests/target/issue-3494/crlf.rs.
The file will have its original line endings in your working directory
```

Author: jyn514

src/tools/rustfmt/.gitattributes

@@ -1,2 +1,2 @@
 # Stop git from showing CRLF tests as modified
-* eol=Unset
+* text=auto eol=Unset