use git checkout -force

In one commit I have changed .gittattributes. During checkout of a this commit on the runner the checkout fails. Checkout force would do the job. why does the checkout fail and is there a way to force the checkout of the runner?

gitlab-ci-multi-runner 1.0.4 (014aa8c)
Using Shell executor...
Running on CODEGEN-PC...
Fetching changes...
HEAD is now at 6d41dfe Merge branch 'f-PV_Sfunc_return' into 'develop'
Checking out 7d664893 as develop...
error: Your local changes to the following files would be overwritten by checkout:
	.gitattributes