bug #54419 Fix TypeError on ProgressBar (Fan2Shrek)

This PR was merged into the 6.4 branch.

Discussion
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Fix TypeError on ProgressBar

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | Fix #54386
| License       | MIT

`ProgressBar->getMessage()` returns null if the message is not defined

Commits
-------

adfe8df Fix TypeError on ProgressBar

src/Symfony/Component/Console/Helper/ProgressBar.php

@@ -183,9 +183,9 @@ public function setMessage(string $message, string $name = 'message'): void
         $this->messages[$name] = $message;
     }
 
-    public function getMessage(string $name = 'message'): string
+    public function getMessage(string $name = 'message'): ?string
     {
-        return $this->messages[$name];
+        return $this->messages[$name] ?? null;
     }
 
     public function getStartTime(): int