docs: Fix link to core beta documentation for ephemeral resources

[austinvalle]

Current docs link to the stable Terraform core docs, but their docs release under the beta version (v1.10.x)

This fixes the links:

• https://developer.hashicorp.com/terraform/language/v1.10.x/resources/ephemeral
• https://developer.hashicorp.com/terraform/language/v1.10.x/resources/ephemeral#referencing-ephemeral-resources