fix(outdated): return array for outdated deps from multiple workspaces

[lukekarrys]

Fixes #6630

[npm-cli-bot]

no statistically significant performance changes detected

timing results

app-large	clean	lock-only	cache-only	modules-only	no-lock	no-cache	no-modules	no-clean	show-version	run-script	cache-only peer-deps	no-clean audit
npm@latest	35.199 ±0.31	11.063 ±0.02	11.972 ±0.08	1.598 ±0.02	1.575 ±0.01	1.302 ±0.00	8.426 ±0.06	1.301 ±0.01	0.144 ±0.00	0.167 ±0.00	14.897 ±0.00	2.109 ±0.06
#7538	33.220 ±1.21	10.808 ±0.03	11.924 ±0.08	1.554 ±0.02	1.560 ±0.00	1.296 ±0.02	8.363 ±0.00	1.324 ±0.04	0.140 ±0.00	0.168 ±0.00	14.874 ±0.17	2.215 ±0.06

app-medium	clean	lock-only	cache-only	modules-only	no-lock	no-cache	no-modules	no-clean	show-version	run-script	cache-only peer-deps	no-clean audit
npm@latest	27.849 ±1.21	8.047 ±0.02	8.954 ±0.00	1.530 ±0.03	1.521 ±0.02	1.431 ±0.00	5.916 ±0.05	1.321 ±0.00	0.140 ±0.00	0.173 ±0.00	9.961 ±0.08	2.003 ±0.01
#7538	27.653 ±0.03	8.061 ±0.03	8.976 ±0.04	1.526 ±0.03	1.524 ±0.00	1.430 ±0.02	5.885 ±0.02	1.313 ±0.01	0.139 ±0.00	0.166 ±0.00	10.035 ±0.01	2.028 ±0.05