Bump docker/build-push-action from 6.12.0 to 6.13.0 #934

Job	Run time
shellcheck	9s
Test scripts (gantry_cleanup_images_spec.sh)	1m 0s
Test scripts running in parallel	3m 22s
Test container	3m 18s
Test scripts (gantry_common_options_spec.sh)	1m 32s
Test scripts (gantry_filters_spec.sh)	52s
Test scripts (gantry_jobs_spec.sh)	51s
Test scripts (gantry_login_docker_config_spec.sh)	57s
Test scripts (gantry_login_negative_spec.sh)	1m 16s
Test scripts (gantry_login_spec.sh)	1m 4s
Test scripts (gantry_manifest_spec.sh)	55s
Test scripts (gantry_notify_spec.sh)	1m 25s
Test scripts (gantry_parallel_spec.sh)	1m 0s
Test scripts (gantry_rollback_spec.sh)	49s
Test scripts (gantry_service_multiple_spec.sh)	35s
Test scripts (gantry_service_no_running_tasks_spec.sh)	54s
Test scripts (gantry_service_single_spec.sh)	56s
Test scripts (gantry_update_options_spec.sh)	56s
Build and push Docker image	0s
	21m 51s

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