Squiz/MultiLineFunctionDeclaration: add tests for arrow function declarations

The Squiz sniff inherits the change from the `PEAR.Functions.FunctionDeclaration` sniff.

This commit adds tests to document the behaviour and safeguard the inherited change.

Author: jrfnl

src/Standards/Squiz/Tests/Functions/MultiLineFunctionDeclarationUnitTest.inc

@@ -302,3 +302,24 @@ new ExceptionMessage(),
     ) {
     }
 }
+
+$arrowNoArgs = fn () => $retrievedfromscope;
+
+$arrowSingleLineArgs = fn (Type $param1, int $param2, string $param3): \ReturnType => $retrievedfromscope;
+
+$arrowMultiLineArgs = fn (
+    $longVar1,
+    $longerVar2,
+    &...$muchLongerVar3
+) => $longVar1;
+
+$arrowNoArgs = fn(  )
+    => $retrievedfromscope;
+
+$arrowSingleLineArgs = fn( Type   $param1  ,   int   $param2, string $param3
+   )  : \ReturnType   => $retrievedfromscope;
+
+$arrowMultiLineArgs = fn (
+    $longVar1, $longerVar2,
+
+  & ...  $muchLongerVar3) => $longVar1;

src/Standards/Squiz/Tests/Functions/MultiLineFunctionDeclarationUnitTest.inc.fixed

@@ -314,3 +314,24 @@ new ExceptionMessage(),
     ) {
     }
 }
+
+$arrowNoArgs = fn () => $retrievedfromscope;
+
+$arrowSingleLineArgs = fn (Type $param1, int $param2, string $param3): \ReturnType => $retrievedfromscope;
+
+$arrowMultiLineArgs = fn (
+    $longVar1,
+    $longerVar2,
+    &...$muchLongerVar3
+) => $longVar1;
+
+$arrowNoArgs = fn (  )
+    => $retrievedfromscope;
+
+$arrowSingleLineArgs = fn ( Type   $param1  ,   int   $param2, string $param3)  : \ReturnType   => $retrievedfromscope;
+
+$arrowMultiLineArgs = fn (
+    $longVar1,
+    $longerVar2,
+    & ...  $muchLongerVar3
+) => $longVar1;

src/Standards/Squiz/Tests/Functions/MultiLineFunctionDeclarationUnitTest.php

@@ -70,6 +70,12 @@ public function getErrorList($testFile='MultiLineFunctionDeclarationUnitTest.inc
                 252 => 1,
                 253 => 1,
                 254 => 1,
+                316 => 1,
+                319 => 1,
+                320 => 1,
+                323 => 1,
+                324 => 1,
+                325 => 2,
             ];
         } else {
             $errors = [