Change check_output to not use the shell equal to True functionality.

What does this MR do?

This MR removes the use of shell=True from several Python subprocess calls. This resolves the Critical security vulnerabilities associated with those lines. The code is not doing a complex shell command where shell=True would be needed, so they should set it to False instead.

What are the relevant issue numbers?

None.

Does this MR meet the acceptance criteria?

• [-] Changelog entry added
• [-] Documentation created/updated for GitLab EE, if necessary
• [-] Documentation created/updated for this project, if necessary
• [-] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
• [-] Job definition updated, if necessary
• [-] Conforms to the code review guidelines
• [-] Conforms to the Go guidelines
• Security reports checked/validated by reviewer