rewrite flaky category test

[cfryanr]

The integration test called TestGetPinnipedCategory has been very flaky in CI lately. I reviewed what it tries to cover and rewrote it. Hopefully this will make it less flaky, and hopefully the new implementation is more clear in what it is trying to cover.

Note that which specific custom APIs should be included in the "pinniped" category is already covered by this other test and so it does not need to be covered by TestGetPinnipedCategory.

I retained the parts of the test which show that listing the resources of the aggregated APIs should work and should always return an empty list, but I rewrote that too.

Release note:

Test-only changes.

NONE

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 30.68%. Comparing base (b50d138) to head (88bcdba).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1992 +/- ## ======================================= Coverage 30.68% 30.68% ======================================= Files 365 365 Lines 60617 60617 ======================================= + Hits 18598 18599 +1 Misses 41482 41482 + Partials 537 536 -1 ```

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