[TXT Registry] Fix Records() case handling

[Sewci0]

There's an issue in Records() function in TXT Registry. When using templated affix, recordType will be passed in lowercase in:

external-dns/registry/txt.go

Lines 140 to 144 in 6a53959

	key := endpoint.EndpointKey{
	DNSName: endpointName,
	RecordType: recordType,
	SetIdentifier: record.SetIdentifier,
	}

This will then fail to match against the computed key with uppercase recordType in:

external-dns/registry/txt.go

Lines 159 to 175 in 6a53959

	key := endpoint.EndpointKey{
	DNSName: dnsName,
	RecordType: ep.RecordType,
	SetIdentifier: ep.SetIdentifier,
	}
	// Handle both new and old registry format with the preference for the new one
	labels, labelsExist := labelMap[key]
	if !labelsExist && ep.RecordType != endpoint.RecordTypeAAAA {
	key.RecordType = ""
	labels, labelsExist = labelMap[key]
	}
	if labelsExist {
	for k, v := range labels {
	ep.Labels[k] = v
	}
	}

Surprisingly it wasn't caught by any of the existing tests. I've added few cases should capture that in the future.

Checklist

• Unit tests updated

[k8s-ci-robot]

Hi @Sewci0. Thanks for your PR.

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[Sewci0]

It's a fix to: #3724. @johngmyers / @szuecs can you please take a look?

[johngmyers]

/ok-to-test
/lgtm
/asssign @szuecs

[johngmyers]

/lgtm

[Sewci0]

/assign @szuecs

[johngmyers]

/approve

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This pull-request has been approved by: johngmyers

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