Fix spec for Conan: latest version of protobuf depends on zlib

What does this MR do?

The integration c job now fails because it installs the latest version of the protobuf package, and package dependencies have changed. See older execution of the job.

What are the relevant issue numbers?

None

Does this MR meet the acceptance criteria?

• [N/A] 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
  • Job definition example
  • CI Templates (to be removed)
  • Vendored CI Templates (also in CE)
  • Ensure that all of the ENV vars supported are propagated to Docker containers upon docker run in job definitions
• Conforms to the code review guidelines
• Security reports checked/validated by reviewer

/cc @adamcohen