Test redis-namespace 1.9.0 compatibility with Ruby 3.2

During Ruby 3.1/3.2 audit (refer to this table and search for the gem name), we discovered that
1.9.0 does not have 3.2 pipeline: https://github.com/resque/redis-namespace/actions/runs/2852374908 Even the latest version does not: https://github.com/resque/redis-namespace/actions/runs/5213265225
May be worth checking manually for 3.2 and also upgrading the upstream

Alternatively, we may want to retest the current version manually with the given Ruby versions.

Team/Group/Domain: Scalability (they will own Redis now)

Actions requested

• Check whether the gem's repo is running CI builds against Ruby 3.1/3.2 already.
  • If not submit an MR/PR to add them
• Browse the gem's issue tracker for any signs of Ruby 3 incompatibilities.
• Check if tests pass locally if there is no Ruby 3.1/3.2 build (see #422680 (closed) for an example of this)
• Think about use cases that may not be well-covered with automated tests we already run. An example could be edge cases that only trigger with specific data being used.
  • Manually test these if possible
• Pay special attention to gems that use C-extensions. These talk to internal MRI APIs that may change across major Ruby releases.