fix tests in eventmesh_test.go

[muralov]

Description

During enabling linting (goerr113) we discovered that Test_reconcileEventMeshSubManager uses require.ErrorAs wrongly. The tests pass internal/controller/operator/eventing/eventmesh_test.go:322 even when the error returned was not the one required. Please check how to use require.ErrorAs and require.ErrorIs. In this require.ErrorIs is probably the right function to use.

Priority critical as the tests could potentially hide errors due to flawed implementation

Acceptance

• enable linting with goerr113 for the entire file
• validate all test cases

[muralov]

I removed the critical importance as business logic is correct, but the test should have been improved.