chore: upgrade ristretto to use generics

[aeneasr]

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Attention: Patch coverage is 78.57143% with 3 lines in your changes missing coverage. Please review.

Project coverage is 74.95%. Comparing base (62ca1e8) to head (648d776).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
...e/authn/authenticator_oauth2_client_credentials.go	66.66%	0 Missing and 1 partial ⚠️
...peline/authn/authenticator_oauth2_introspection.go	66.66%	0 Missing and 1 partial ⚠️
pipeline/mutate/mutator_hydrator.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1195      +/-   ##
==========================================
- Coverage   75.43%   74.95%   -0.48%     
==========================================
  Files          86       85       -1     
  Lines        4063     4177     +114     
==========================================
+ Hits         3065     3131      +66     
- Misses        724      766      +42     
- Partials      274      280       +6     

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