atlasaction: move github client to internal package #1334

Job	Run time
migrate-down	19s
golangci-lint	17s
migrate-test	20s
monitoring	31s
schema-apply (lint-review)	10s
schema-plan	9s
schema-apply (on-the-fly, true)	9s
schema-plan-approve	0s
schema-push	14s
schema-apply (remote-repo, atlas://atlas-action/plans/20240910183610, atlas://atlas-action?tag=e2e)	12s
schema-test	9s
schema-apply (local-plan, file://20240910173744.plan.hcl)	9s
shim-e2e	7s
shim	12s
schema-apply (multiple-envs, file://20240910173744.plan.hcl)	10s
unit-tests	1m 16s
schema-apply (legacy, v0.27.0, true)	9s
	4m 33s

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