Make ui-fulldeps/update-references executable
When a ui-fulldeps comparison fails it suggests running update-references.sh:
```
src/test/ui-fulldeps/update-references.sh 'rust/build/x86_64-apple-darwin/test/ui-fulldeps' 'resolve-error.rs'
```
This does not work as update-references.sh isn't executable. The other update-references.sh in the ui directory is already executable so this looks like an oversight.
5d9d5ea712