go.mod: bump golang.org/x/net from 0.14.0 to 0.15.0 #276

Job	Run time
CI matrix / Assert PR branch is ahead	8s
Makefile / Assert PR branch is ahead	9s
CI matrix / Lint codebase (go-ci-oldstable, false)	51s
CI matrix / Lint codebase (go-ci-stable, false)	1m 1s
CI matrix / Lint codebase (go-ci-unstable, true)	1m 9s
CI matrix / Build codebase (go-ci-oldstable, false)	39s
CI matrix / Build codebase (go-ci-stable, false)	40s
CI matrix / Build codebase (go-ci-unstable, true)	1m 0s
CI matrix / Run tests (go-ci-oldstable, false)	41s
CI matrix / Run tests (go-ci-stable, false)	43s
CI matrix / Run tests (go-ci-unstable, true)	49s
CI matrix / Optional Linting / Assert PR branch is ahead	6s
Makefile / Lint codebase using Makefile	0s
Makefile / Build codebase using Makefile quick recipe	49s
Makefile / Build codebase using Makefile all recipe	0s
CI matrix / Optional Linting / Lint codebase using optional linters	0s
	8m 45s

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