[CI] Fix test-cta-valgrind failures related to JWT authentication

Description

This commit fixes the grpc JWT auth-related failures in test-cta-valgrind by adding to the suppressions list the produced errors about potential deadlocks. Given that

1. in the stress test, we did not see any failures of the sort and
2. we are not doing anythig weird with the jwt-cpp library, but rather using it in the way it's supposed to be used for token validation,

we think it is safe to suppress these errors.

Checklist

• Documentation reflects the changes made.
• Merge Request title is clear, concise, and suitable as a changelog entry. See our contributing docs

References

Closes #1279 (closed)