dependabot-automerge.yml: add `GH_TOKEN` #468

Job	Run time
docker-master	1s
build-js-of-ocaml	1s
build-wasm-of-ocaml	1s
validate-docker-${{ matrix.env.COQ_VERSION }}	1s
generated-files	1s
publish-standalone-dry-run	1s
standalone-haskell	1s
test-amd64	1s
test-standalone	1s
deploy-js-wasm-of-ocaml	1s
docker-check-all	1s
	11s

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