workflows: update and pin node LTS versions #243

Job	Run time
test / Test Fastify Integration	0s
test / Check Licenses	30s
test / Dependency Review	6s
test / Lint Code	0s
test / Test (16, macos-latest)	1m 10s
test / Test (16, ubuntu-latest)	29s
test / Test (16, windows-latest)	1m 28s
test / Test (18, macos-latest)	1m 5s
test / Test (18, ubuntu-latest)	40s
test / Test (18, windows-latest)	1m 6s
test / Test (20, macos-latest)	1m 3s
test / Test (20, ubuntu-latest)	43s
test / Test (20, windows-latest)	1m 16s
test / Automerge Dependabot PRs	0s
	9m 36s

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