Update Dependabot config to monitor both branches #47

Job	Run time
CI matrix / Assert PR branch is ahead	3s
Makefile / Assert PR branch is ahead	2s
Makefile / Lint codebase using Makefile	49s
Makefile / Build codebase using Makefile quick recipe	31s
Makefile / Build codebase using Makefile all recipe	0s
CI matrix / Run tests (go-ci-oldstable, false)	25s
CI matrix / Run tests (go-ci-stable, false)	34s
CI matrix / Run tests (go-ci-unstable, true)	30s
CI matrix / Lint codebase (go-ci-oldstable, false)	32s
CI matrix / Lint codebase (go-ci-stable, false)	37s
CI matrix / Lint codebase (go-ci-unstable, true)	39s
CI matrix / Build codebase (go-ci-oldstable, false)	19s
CI matrix / Build codebase (go-ci-stable, false)	30s
CI matrix / Build codebase (go-ci-unstable, true)	28s
CI matrix / Optional Linting / Assert PR branch is ahead	6s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-oldstable, true)	29s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-stable, true)	39s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-unstable, true)	33s
	7m 46s

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