chore: add workflow to update pg_upgrade binary nix flake version on-demand #1068

Job	Run time
test-all-in-one (self-hosted, X64, amd64)	2m 33s
test-ami (arm-runner, arm64, focal, 20.04, neoverse-n1)	36m 8s
test-all-in-one (arm-runner, arm64)	2m 49s
	41m 30s

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