lint

CI: update Go (1.26); mark several tests flaky #2353

Job	Run time
other / yaml \| shell	6s
project checks / commits, licenses...	1m 27s
build for / go canary	7s
build for / go 1.26	7m 52s
go / windows	2m 25s
go / freebsd	2m 32s
build for / go 1.25	7m 18s
go / darwin	2m 24s
go / linux (go canary)	6s
go / linux	2m 28s
	26m 45s

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