Update rack to 2.0.6

What does this MR do?

Updates rack to 2.0.6 to address the security vulnerability assigned as CVE-2018-16471.

What are the relevant issue numbers?

Closes #54201 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [n/a] Documentation created/updated
• [n/a] Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [n/a] Conforms to the database guides
• [n/a] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.