Update Terraform exoscale to ~> 0.26

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
exoscale (source)	required_provider	minor	~> 0.25 -> ~> 0.26

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Release Notes

exoscale/terraform-provider-exoscale

### [`v0.26.0`](https://togithub.com/exoscale/terraform-provider-exoscale/blob/master/CHANGELOG.md#​0260-August-12-2021) [Compare Source](https://togithub.com/exoscale/terraform-provider-exoscale/compare/v0.25.0...v0.26.0) FEATURES: - **New Resource:** `exoscale_database` (BETA) IMPROVEMENTS: - `exoscale_sks_nodepool`: add support for Private Networks ([#​114](https://togithub.com/exoscale/terraform-provider-exoscale/issues/114)) - `exoscale_sks_cluster`: add support for auto-upgrades - Upgrade to Terraform SDK v2

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