Update ruby version in FOSS specs to 3.0

What does this MR do?

Updates ruby version in FOSS specs to 3.0 since Ruby 2.5 was just EOL'ed on 2021-03-31.

EE part: !59229 (merged)

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 not included a changelog entry because ~"technical debt" in test .
• Code review guidelines
• Style guides
• Separation of EE specific content