Bump docker/build-push-action from 6.12.0 to 6.13.0 #109

Job	Run time
shellcheck	10s
Test scripts (gantry_cleanup_images_spec.sh)	57s
Test container	3m 37s
Test scripts (gantry_common_options_spec.sh)	1m 41s
Test scripts running in parallel	3m 20s
Test scripts (gantry_filters_spec.sh)	47s
Test scripts (gantry_jobs_spec.sh)	42s
Test scripts (gantry_login_docker_config_spec.sh)	58s
Test scripts (gantry_login_negative_spec.sh)	1m 17s
Test scripts (gantry_login_spec.sh)	1m 3s
Test scripts (gantry_manifest_spec.sh)	55s
Test scripts (gantry_notify_spec.sh)	1m 19s
Test scripts (gantry_parallel_spec.sh)	1m 0s
Test scripts (gantry_rollback_spec.sh)	49s
Test scripts (gantry_service_multiple_spec.sh)	41s
Test scripts (gantry_service_no_running_tasks_spec.sh)	53s
Test scripts (gantry_service_single_spec.sh)	56s
Test scripts (gantry_update_options_spec.sh)	54s
	21m 59s

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