set file_github_issue true for sleuthkit

[simsong]

We would like to have Sleuthkit issues reported on github.

Thank you.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[github-actions]

simsong is a new contributor to projects/sleuthkit. The PR must be approved by known contributors before it can be merged. The past contributors are: joachimmetz, DonggeLiu, inferno-chromium, alsophian

[joachimmetz]

I cannot update reviewer of this PR, but I have discussed the change with @simsong and made him aware of the trade offs (https://google.github.io/oss-fuzz/faq/#why-do-you-use-a-different-issue-tracker-for-reporting-bugs-in-oss-projects) . Config change to enable report to github LGTM