Bump golangci-lint to 2.6.0

[xrstf]

Summary

This is just maintenance. I also bumped logcheck because 0.9 doesn't work on Go 1.25 systems.

gocritic now complains about the misplaced Deprecation notices, and after fixing them, I had to adjust a bit of code in our codebase. However I did not remove the deprecated CreateSheriff, even though it was meant to be deprecated allll the way back in #1642 (2022). But since that never worked, nobody noticed and so I would declare today the official deprecation day 😁

What Type of PR Is This?

/kind chore

Release Notes

NONE

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@xrstf: 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-kcp-test-integration	52db8f2	link	true	/test pull-kcp-test-integration

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