Update ubuntu Docker tag to v26

[red-hat-konflux]

This PR contains the following updates:

Package	Type	Update	Change
ubuntu	final	major	24.04 → 26.04
ubuntu	stage	major	24.04 → 26.04

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

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Documentation

Find out how to configure dependency updates in MintMaker documentation or see all available configuration options in Renovate documentation.

[coderabbitai]

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✨ Finishing Touches

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[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: red-hat-konflux[bot]
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[openshift-ci]

Hi @red-hat-konflux[bot]. Thanks for your PR.

I'm waiting for a openshift member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

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