fix: pass context to @netlify/build

[ehmicky]

Fixes #4403

The context was missing as a parameter to @netlify/build.

---

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[github-actions]

📊 Benchmark results

Comparing with a4eb14d

Package size: 443 MB

(no change)

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└───┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴──>
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Legend

• T-30 (a4eb14d): 443 MB
• T-29 (80704fa): 443 MB
• T-28 (5232a86): 443 MB
• T-27 (ea2a1e0): 443 MB
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• T-21 (eecb146): 443 MB
• T-20 (550c5c0): 443 MB
• T-19 (b3f0522): 443 MB
• T-18 (983b2a5): 443 MB
• T-17 (6729dfd): 443 MB
• T-16 (bfadc76): 443 MB
• T-15 (870644f): 443 MB
• T-14 (c78a716): 443 MB
• T-13 (1870e54): 443 MB
• T-12 (4d58a44): 443 MB
• T-11 (3b7765c): 443 MB
• T-10 (88985c4): 443 MB
• T-9 (110eed6): 443 MB
• T-8 (cd3787c): 443 MB
• T-7 (d9f62e0): 443 MB
• T-6 (fad5ef6): 443 MB
• T-5 (5ea7686): 447 MB
• T-4 (483f51a): 447 MB
• T-3 (7ef657d): 447 MB
• T-2 (2decc3e): 447 MB
• T-1 (69261cd): 443 MB
• T (current commit): 443 MB