Replaced reflect.DeepEqual with cmp.Diff in Go tests

[tariq-hasan]

What this PR does / why we need it: This PR replaces reflect.DeepEqual with cmp.Diff in all the tests.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #2268

Checklist:

• Docs included if any changes are user facing

[tenzen-y]

Could you apply the same approach the same as my comment to other places?

[tenzen-y]

We must define errors, and compare expected and wanted errors and values.

Define errors:

katib/pkg/util/v1beta1/katibconfig/config.go

Lines 38 to 42 in 6fb9157

	var (
	ErrKatibConfigNil = fmt.Errorf("failed to parse katib-config.yaml in ConfigMap: %s", consts.KatibConfigMapName)
	ErrInvalidGVKFormat = errors.New("invalid GroupVersionKinds")
	ErrTrialResourcesAreEmpty = errors.New("trialResources are empty")
	)

Compare Errors:

katib/pkg/util/v1beta1/katibconfig/config_test.go

Lines 72 to 74 in 6fb9157

	if diff := cmp.Diff(tc.wantError, err, cmpopts.EquateErrors()); len(diff) != 0 {
	t.Errorf("Unexpected error from TrialResourcesToGVKs (-want,+got):\n%s", diff)
	}

[tariq-hasan]

Sounds good. I am creating a separate PR given that file-metricscollector_test.go has already been updated in #2274.

[google-oss-prow]

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