Remove executable bits from documentation images

The build in https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/194484356 was failing.

Remove executable bits from documentation images
The build in https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/194484356 was failing.
327f9ba7 · Stan Hu · b9e6e725 · 327f9ba7 · 327f9ba7 · 327f9ba7
--- a/doc/ci/introduction/img/job_running.png
+++ b/doc/ci/introduction/img/job_running.png
--- a/doc/ci/introduction/img/pipeline_status.png
+++ b/doc/ci/introduction/img/pipeline_status.png
--- a/doc/ci/introduction/img/rollback.png
+++ b/doc/ci/introduction/img/rollback.png