Generic/RequireStrictTypes: add extra tests

These tests safeguard the following, which is already handled correctly by the sniff:
* Execution directives are case-insensitive in PHP.
* The sniff should ignore docblocks at the top of the file.

Author: jrfnl

src/Standards/Generic/Tests/PHP/RequireStrictTypesUnitTest.3.inc

@@ -0,0 +1,5 @@
+<?php
+
+declare( Strict_Types = 1 );
+
+// some code

src/Standards/Generic/Tests/PHP/RequireStrictTypesUnitTest.4.inc

@@ -0,0 +1,10 @@
+<?php
+/**
+ * Very
+ * Long
+ * Docblock
+ */
+
+declare(strict_types=1);
+
+// some code

src/Standards/Generic/Tests/PHP/RequireStrictTypesUnitTest.php

@@ -28,12 +28,13 @@ class RequireStrictTypesUnitTest extends AbstractSniffUnitTest
     public function getErrorList($testFile='')
     {
         switch ($testFile) {
-        case 'RequireStrictTypesUnitTest.1.inc':
+        case 'RequireStrictTypesUnitTest.2.inc':
+            return [1 => 1];
+
+        default:
             return [];
         }
 
-        return [1 => 1];
-
     }//end getErrorList()