bump Go to 1.26, run modernize

[majewsky]

I had to run go-makefile-maker manually here. The go-m-m pipeline cannot commit this change because it then complains about the new fixable idioms, but also I cannot fix the idioms without raising the go version.

[github-actions]

Merging this branch will decrease overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/sapcc/maintenance-controller/controllers	85.42% (ø)
github.com/sapcc/maintenance-controller/plugin/impl	81.41% (-0.02%)	👎

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/sapcc/maintenance-controller/plugin/impl/hypervisor.go	94.68% (-0.06%)	94 (-1)	89 (-1)	5	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/sapcc/maintenance-controller/controllers/node_controller_test.go