Attempt to fix the bug

Author: pincher2012

src/Util/YamlSourceManipulator.php

@@ -544,7 +544,15 @@ private function advanceBeyondMultilineArrayLastItem(): void
         }
 
         $nextLineBreak = $this->findNextLineBreak($this->currentPosition);
-        if ('}' === trim(substr($this->contents, $this->currentPosition, $nextLineBreak - $this->currentPosition))) {
+        if (false === $nextLineBreak) {
+            $this->log('The last line, going to EOL');
+            $this->advanceToEndOfLine();
+
+            return;
+        }
+
+        $lastSymbolBeforeLineBreak = trim(substr($this->contents, $this->currentPosition, $nextLineBreak - $this->currentPosition));
+        if (\in_array($lastSymbolBeforeLineBreak, ['}', ']'], true)) {
             $this->log('The line ends with an array closing brace, going to EOL');
             $this->advanceToEndOfLine();
         }

tests/Util/yaml_fixtures/add_item_to_array_after_array.test

@@ -9,4 +9,4 @@ framework:
     messenger:
         routing:
             App\Messages\OldMessage: [ transport1, transport2 ]
-            App\Messages\NewMessage: async
+            App\Messages\NewMessage: async

tests/Util/yaml_fixtures/add_item_to_array_after_array_trailing_newline.test

@@ -0,0 +1,13 @@
+framework:
+    messenger:
+        routing:
+            App\Messages\OldMessage: [ transport1, transport2 ]
+
+===
+$data['framework']['messenger']['routing']['App\Messages\NewMessage'] = 'async';
+===
+framework:
+    messenger:
+        routing:
+            App\Messages\OldMessage: [ transport1, transport2 ]
+            App\Messages\NewMessage: async