feature #50842 Add missing return types to magic methods (wouterj)

This PR was merged into the 6.4 branch.

Discussion
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Add missing return types to magic methods

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | yes
| Tickets       | -
| License       | MIT
| Doc PR        | -

I promise, these 72 methods really are the last methods that did not have a return type already 🙃

Commits
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6b270010c4 Add missing return types to magic methods

Author: nicolas-grekas

UnicodeString.php

@@ -338,6 +338,9 @@ public function startsWith(string|iterable|AbstractString $prefix): bool
         return $prefix === grapheme_extract($this->string, \strlen($prefix), \GRAPHEME_EXTR_MAXBYTES);
     }
 
+    /**
+     * @return void
+     */
     public function __wakeup()
     {
         if (!\is_string($this->string)) {