canary: bump golang from 1.20.13 to 1.21rc4 in /dependabot/docker/go #426

Job	Run time
CI matrix / Assert PR branch is ahead	4s
Makefile / Assert PR branch is ahead	4s
CI matrix / Run tests (go-ci-oldstable, false)	27s
CI matrix / Lint codebase (go-ci-oldstable, false)	32s
CI matrix / Run tests (go-ci-stable, false)	32s
CI matrix / Lint codebase (go-ci-stable, false)	32s
CI matrix / Run tests (go-ci-unstable, true)	27s
CI matrix / Lint codebase (go-ci-unstable, true)	32s
CI matrix / Build codebase (go-ci-oldstable, false)	38s
CI matrix / Build codebase (go-ci-stable, false)	27s
CI matrix / Build codebase (go-ci-unstable, true)	32s
CI matrix / Optional Linting / Assert PR branch is ahead	4s
Makefile / Build codebase using Makefile quick recipe	31s
Makefile / Build codebase using Makefile all recipe	0s
Makefile / Lint codebase using Makefile	0s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-oldstable, true)	27s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-stable, true)	28s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-unstable, true)	39s
	6m 56s

Provide feedback