test(signature): guard unsupported EC curve widths

Assisted-by: GitHub Copilot Coding Agent:gpt-5.6-terra

Author: Copilot

tests/lib/Security/Signature/Rfc9421/AlgorithmTest.php

@@ -198,6 +198,7 @@ private static function coordinateSizeForCurve(string $curve): int {
 		return match ($curve) {
 			'P-256' => 32,
 			'P-384' => 48,
+			default => throw new \InvalidArgumentException('unsupported EC curve: ' . $curve),
 		};
 	}