minor symfony#28407 Add missing UPGRADE-4.2 entry for Controller deprecation (chalasr)

This PR was merged into the 4.2-dev branch.

Discussion
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Add missing UPGRADE-4.2 entry for Controller deprecation

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Forgot in symfony#28243, removal documented in UPGRADE-5.0

Commits
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cc23f5d Add missing UPGRADE-4.2 entry for Controller deprecation

Author: nicolas-grekas

UPGRADE-4.2.md

@@ -84,6 +84,7 @@ FrameworkBundle
    this will generate 404s for non-UTF-8 URLs, which are incompatible with you app anyway,
    and will allow dumping optimized routers and using Unicode classes in requirements.
  * Added support for the SameSite attribute for session cookies. It is highly recommended to set this setting (`framework.session.cookie_samesite`) to `lax` for increased security against CSRF attacks.
+ * The `Controller` class has been deprecated, use `AbstractController` instead.
 
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