Use set_error_handler() to consume iconv warning under PHPUnit.

Author: dereuromark

src/View/CsvView.php

@@ -485,15 +485,15 @@ protected function _transcode(string $csv, string $dataEncoding, string $csvEnco
                 default => $csvEncoding,
             };
             // iconv() emits an E_NOTICE / E_WARNING immediately before returning
-            // false on unconvertible input. Suppress just for this call so we
-            // surface the failure via our own (strict-mode) exception below
-            // rather than as two near-duplicate signals.
-            $previousReporting = error_reporting();
-            error_reporting($previousReporting & ~(E_NOTICE | E_WARNING));
+            // false on unconvertible input. Install a no-op handler for the
+            // duration of the call so we surface the failure via our own
+            // (strict-mode) exception below rather than as two near-duplicate
+            // signals. PHPUnit's own error handler is restored on `finally`.
+            set_error_handler(static fn(): bool => true, E_NOTICE | E_WARNING);
             try {
                 $converted = iconv($dataEncoding, $targetSpec, $csv);
             } finally {
-                error_reporting($previousReporting);
+                restore_error_handler();
             }
             if ($converted === false) {
                 if ($mode === static::TRANSCODING_MODE_STRICT) {