Update Ruby from 2.5 to 2.7 in Dockerfile templates

What does this MR do?

Updates Ruby from 2.5 to 2.7 in Dockerfile templates.

Part of #327579 (closed)

Screenshots (strongly suggested)

n/a

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
• Code review guidelines
• Style guides
• Separation of EE specific content