tee: allow multiple -a flags #10293

Performance Regression: -27.39%

❌ 7 regressed benchmarks
✅ 275 untouched benchmarks
⏩ 38 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

	Mode	Benchmark	`BASE`	`HEAD`	Efficiency
❌	Memory	`sort_unique_locale[500000]`	33.6 MB	39.8 MB	-15.5%
❌	Memory	`sort_ascii_only[500000]`	22.2 MB	28.3 MB	-21.77%
❌	Memory	`sort_long_line[160000]`	712.6 KB	981.4 KB	-27.39%
❌	Memory	`sort_mixed_data[500000]`	22.9 MB	27.1 MB	-15.71%
❌	Memory	`sort_numeric[500000]`	75.5 MB	79.2 MB	-4.67%
❌	Memory	`sort_accented_data[500000]`	22.1 MB	28.3 MB	-21.79%
❌	Memory	`sort_key_field[500000]`	47.8 MB	51.8 MB	-7.62%

_{Comparing sylvestre:tee-a (14c517e) with main (f2bec7b)}

38 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩