Fix invalid SSL certificate errors on Drone CI service

What does this MR do?

Handle invalid SSL certificate errors while calculating the reactive cache for the Drone CI service. For more information see https://gitlab.com/gitlab-org/gitlab-ce/issues/64176#note_188897115

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Related issues

#64176 (closed)

/cc @stanhu @smcgivern