fix: less flaky rule tests

[hperl]

Instead of (flaky) fixed sleeps, we now use assert.Eventually
to wait until the rule changes were propagated.

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 green light (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

Merging #973 (d576202) into master (c4836f5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #973   +/-   ##
=======================================
  Coverage   66.01%   66.01%           
=======================================
  Files         106      106           
  Lines        4723     4723           
=======================================
  Hits         3118     3118           
  Misses       1324     1324           
  Partials      281      281           

Impacted Files	Coverage Δ
internal/httpclient/models/health_status.go	0.00% <ø> (ø)
internal/httpclient/models/json_web_key.go	0.00% <ø> (ø)
internal/httpclient/models/json_web_key_set.go	0.00% <ø> (ø)
internal/httpclient/models/rule.go	0.00% <ø> (ø)
internal/httpclient/models/rule_handler.go	0.00% <ø> (ø)
internal/httpclient/models/rule_match.go	0.00% <ø> (ø)
internal/httpclient/models/upstream.go	0.00% <ø> (ø)
internal/httpclient/models/version.go	0.00% <ø> (ø)

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