Bump docker/build-push-action from 6.0.0 to 6.3.0 #58

Job	Run time
shellcheck	8s
Run tests (gantry_cleanup_images_spec.sh)	2m 1s
Run tests (gantry_common_options_spec.sh)	1m 39s
Run tests (gantry_filters_spec.sh)	1m 13s
Run tests (gantry_login_spec.sh)	1m 59s
Run tests (gantry_manifest_spec.sh)	1m 47s
Run tests (gantry_notify_spec.sh)	1m 44s
Run tests (gantry_parallel_spec.sh)	2m 0s
Run tests (gantry_rollback_spec.sh)	59s
Run tests (gantry_service_multiple_spec.sh)	1m 43s
Run tests (gantry_service_no_running_tasks_spec.sh)	1m 33s
Run tests (gantry_service_single_spec.sh)	1m 24s
Run tests (gantry_update_options_spec.sh)	1m 46s
	19m 56s

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