(NFC) DateTest - Speed up ~55%

Before: On local i3-12100, takes ~90s (avg over 2 runs)

After: On local i3-12100, take ~40s (avg over 2 runs)

tests/phpunit/CRM/Utils/DateTest.php

@@ -26,6 +26,14 @@
  */
 class CRM_Utils_DateTest extends CiviUnitTestCase {
 
+  /**
+   * Set up for tests.
+   */
+  public function setUp(): void {
+    $this->useTransaction();
+    parent::setUp();
+  }
+
   /**
    * Used by testGetFromTo
    */