Update go to 1.26 (minor)

[gardener-ci-robot]

This PR contains the following updates:

Package	Type	Update	Change
go	uses-with	minor	1.25 → 1.26
golang	stage	minor	1.25.5 → 1.26.0

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Release Notes

actions/go-versions (go)

v1.26.0: 1.26.0

Compare Source

Go 1.26.0

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Configuration

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• If you want to rebase/retry this PR, check this box

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Release note:

The following dependencies have been updated:
- `go` from `1.25.7` to `1.26.0`. [Release Notes](https://redirect.github.com/go/releases/tag/1.26.0)
- `golang` from `1.25.5` to `1.26.0`. 

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[gardener-prow]

@gardener-ci-robot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-gardener-e2e-kind	1378761	link	true	/test pull-cluster-api-provider-gardener-e2e-kind

Full PR test history. Your PR dashboard. Command help for this repository.
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