fix typo on README.md about .Values.singleCA.enable

[kudalumping12]

Describe the Change You Would Like

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there is some typo on https://github.com/puppetlabs/puppetserver-helm-chart/tree/master?tab=readme-ov-file#using-single-ca

it supposed to be .Values.singleCA.enabled instead .Values.singleCA.enable for enable singleCA

[davidphay]

Hello @kudalumping12, can you please updeate the Chart.yaml and the changelog, then we will able to merge it !

Thanks :)