Use new script path as default

The default location for CI scripts is now `scripts` (it used to be
`.gitlab/scripts`). Update the default values for `FETCH_SCRIPT` in
`Collate-Results` and `complete-lava-job`.

When they are updated, projects which still use the old location must
either move their scripts or override the value of `FETCH_SCRIPT`.

Changelog: other
Signed-off-by: Adam Johnston <adam.johnston@linaro.org>