Fixed logic to choose whether to use filter or filters for a trigger

[Cali0707]

Currently, the logic to select whether to use the trigger.Spec.Filter vs. trigger.Spec.Filters is not correct. If I have provided a trigger.Spec.Filter, and no trigger.Spec.Filters, then currently we would still apply the trigger.Spec.Filters and return filter.NoFilter, instead of applying my trigger.Spec.Filter. This leads to incorrect event processing.

Proposed Changes

• Fix the logic used to apply the filter vs. the filters field

Pre-review Checklist

• At least 80% unit test coverage
• E2E tests for any new behavior
• Docs PR for any user-facing impact
• Spec PR for any new API feature
• Conformance test for any change to the spec

Release Note

:bug: The filters field now only overrides the filter field on a trigger if there are filters in the filters field.

Docs

[knative-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[Cali0707]

/cc @pierDipi @creydr @Leo6Leo
This should fix the failing tests on #7243

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: +0.04% 🎉

Comparison is base (b704ab1) 77.54% compared to head (ac3c95c) 77.59%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7286      +/-   ##
==========================================
+ Coverage   77.54%   77.59%   +0.04%     
==========================================
  Files         249      249              
  Lines       13407    13404       -3     
==========================================
+ Hits        10397    10401       +4     
+ Misses       2485     2479       -6     
+ Partials      525      524       -1     

Files Changed	Coverage Δ
pkg/broker/filter/filter_handler.go	68.99% <66.66%> (+1.82%)	⬆️

... and 2 files with indirect coverage changes

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[creydr]

Hey @Cali0707,
thanks for working on this. Could we add a test, to prevent this in future?

[Cali0707]

/cc @creydr

[creydr]

/lgtm

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Cali0707, creydr

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