[renovate]

This PR contains the following updates:

Package	Type	Update	Change
ubuntu	github-runner	major	24.04 → 26.04

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[yegor256]

The actionlint check fails because of this upgrade, not because of the default branch.
The default branch is green, and every other job in this pull request passes on the ubuntu-26.04 runner.

actionlint reports the same error for all seven workflows, for example:

.github/workflows/actionlint.yml:16:14: label "ubuntu-26.04" is unknown. available labels are ... "ubuntu-24.04", "ubuntu-24.04-arm", "ubuntu-22.04", ... [runner-label]

The workflow downloads the latest actionlint, and neither its latest release (v1.7.12) nor its main branch knows the ubuntu-26.04 label yet (see rule_runner_label.go).
Upstream tracks this in rhysd/actionlint#682, and rhysd/actionlint#683 and rhysd/actionlint#743 would fix it, but none of them is merged.

This pull request is blocked until actionlint releases a version that knows ubuntu-26.04.
After that, rebasing or re-running the check should turn it green, and the pull request can be merged.
Declaring ubuntu-26.04 as a self-hosted runner label in .github/actionlint.yaml would also silence the error, but that hides a real check, so I suggest waiting for the upstream fix instead.