Squiz/NonExecutableCode: bug fix - expressions in PHP 7.4 arrow functions

PHP 7.4 introduced arrow functions. The `T_EXIT` token can be used in those without affecting the code following it.

See: https://3v4l.org/gSrt4#veol

Fixed now.

Includes unit test.

Author: jrfnl

src/Standards/Squiz/Sniffs/PHP/NonExecutableCodeSniff.php

@@ -78,7 +78,12 @@ public function process(File $phpcsFile, $stackPtr)
             if ($tokens[$prev]['code'] === T_COALESCE || $tokens[$prev]['code'] === T_COALESCE_EQUAL) {
                 return;
             }
-        }
+
+            // Expressions are allowed in arrow functions.
+            if ($tokens[$prev]['code'] === T_FN_ARROW) {
+                return;
+            }
+        }//end if
 
         // Check if this token is actually part of a one-line IF or ELSE statement.
         for ($i = ($stackPtr - 1); $i > 0; $i--) {

src/Standards/Squiz/Tests/PHP/NonExecutableCodeUnitTest.1.inc

@@ -342,5 +342,11 @@ function exitExpressionsWithNullCoalesce() {
     echo 'still executable';
 }
 
+// Inline expressions are allowed in arrow functions.
+function exitExpressionsInArrowFunction() {
+    $callable = fn() => die();
+    echo 'still executable';
+}
+
 // Intentional syntax error.
 return array_map(