bug #48870 [Clock] Fix unitialized variable (fabpot)

This PR was merged into the 6.3 branch.

Discussion
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[Clock] Fix unitialized variable

| Q             | A
| ------------- | ---
| Branch?       | 6.3
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | n/a

Commits
-------

2df462301c [Clock] Fix unitialized variable

Author: fabpot

Clock.php

@@ -46,14 +46,14 @@ public static function set(PsrClockInterface $clock): void
 
     public function now(): \DateTimeImmutable
     {
-        $now = ($this->clock ?? self::$globalClock)->now();
+        $now = ($this->clock ?? self::get())->now();
 
         return isset($this->timezone) ? $now->setTimezone($this->timezone) : $now;
     }
 
     public function sleep(float|int $seconds): void
     {
-        $clock = $this->clock ?? self::$globalClock;
+        $clock = $this->clock ?? self::get();
 
         if ($clock instanceof ClockInterface) {
             $clock->sleep($seconds);