Use `go.mod` as source of Go version number for workflows #1362

Job	Run time
run-determination	1s
check-style (./)	23s
check-outdated (./)	8s
check-style (docsgen)	16s
check-outdated (docsgen)	11s
check-errors (./)	15s
check-style (ruledocsgen)	10s
check-config (./)	24s
check-outdated (ruledocsgen)	12s
check-errors (docsgen)	13s
check-config (docsgen)	25s
check-errors (ruledocsgen)	14s
check-config (ruledocsgen)	17s
check-formatting (./)	13s
check-formatting (docsgen)	14s
check-formatting (ruledocsgen)	11s
	3m 47s

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