Update httparty for Ruby 3 readiness

We currently use v0.16.4 of httparty. This gem is used fairly widely throughout gitlab-rails and also supports the Gitlab::HTTP wrapper.

This version may not be Ruby 3 ready:

Post-install message from contracts:

    0.16.x will be the supporting Ruby 2.x and be feature frozen (only fixes will be released)
    For Ruby 3.x use 0.17.x or later (might not be released yet)

The project runs an upstream Ruby 3 build as of https://github.com/jnunemaker/httparty/pull/737.