fix: ignore implicit workspaces for completion

[wraithgar]

Closes#5895

[npm-cli-bot]

found 1 benchmarks with statistically significant performance improvements

• app-medium: clean

timing results

app-large	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	49.539 ±2.43	20.780 ±0.21	19.241 ±0.19	22.568 ±1.21	3.535 ±0.03	3.496 ±0.04	2.848 ±0.03	13.422 ±0.12	2.851 ±0.05	4.240 ±0.28
#5932	52.750 ±7.51	20.475 ±0.08	18.947 ±0.08	21.724 ±0.41	3.590 ±0.11	3.498 ±0.10	2.735 ±0.01	13.454 ±0.10	2.762 ±0.02	4.117 ±0.25

app-medium	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	38.257 ±0.25	16.266 ±0.05	14.926 ±0.13	16.114 ±0.80	3.173 ±0.02	3.223 ±0.07	2.951 ±0.02	10.213 ±0.09	2.690 ±0.01	3.737 ±0.06
#5932	33.851 ±0.01	15.924 ±0.01	14.644 ±0.09	15.869 ±0.57	3.187 ±0.01	3.153 ±0.02	2.861 ±0.15	10.339 ±0.13	2.590 ±0.07	3.545 ±0.00