fix: set provider_visibility back to public to workaround provider bug

[ocofaigh]

Description

set provider_visibility back to public to workaround provider bug: IBM-Cloud/terraform-provider-ibm#5828

I also created an issue to plug the test gap which allowed the bug to get into the DA: #235

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[ocofaigh]

/run pipeline

[ocofaigh]

/run pipeline

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🎉 This PR is included in version 2.6.1 🎉

The release is available on:

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• v2.6.1

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