fix: fix dialyzer types for `AshGraphql.Type` #799

Job	Run time
ash-ci / mix deps.get	14s
ash-ci / mix hex.audit	15s
ash-ci / MIX_ENV=dev mix.compile	34s
ash-ci / MIX_ENV=test mix.compile	38s
ash-ci / mix spark.formatter --check	35s
ash-ci / mix format --check-formatted	33s
ash-ci / mix sobelow	48s
ash-ci / mix spark.cheat_sheets --check	34s
ash-ci / mix credo --strict	40s
ash-ci / mix dialyzer	3m 58s
ash-ci / mix test	1m 16s
ash-ci / mix deps.unlock --check-unused	36s
ash-ci / Release	0s
	10m 41s

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