minor symfony#20691 [Serializer] Add deprecation missing from UPGRADE files (ogizanagi, javiereguiluz)

This PR was merged into the 3.2 branch.

Discussion
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[Serializer] Add deprecation missing from UPGRADE files

| Q             | A
| ------------- | ---
| Branch?       | 3.2
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no, simply mention one in upgrade files
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

Commits
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d681c1a Lines length should be 80 or less characters
597bbdc Lines length should be 80 or less characters
4514c1b [Serializer] Add deprecation missing from UPGRADE files

Author: fabpot

UPGRADE-3.2.md

@@ -112,6 +112,13 @@ HttpKernel
    ```
    Surrogate-Capability: symfony="ESI/1.0"
 
+Serializer
+----------
+
+ * Method `AbstractNormalizer::instantiateObject()` will have a 6th
+   `$format = null` argument in Symfony 4.0. Not defining it when overriding
+   the method is deprecated.
+
 TwigBridge
 ----------
 

UPGRADE-4.0.md

@@ -170,6 +170,10 @@ Serializer
  * The ability to pass a Doctrine `Cache` instance to the `ClassMetadataFactory`
    class has been removed. You should use the `CacheClassMetadataFactory` class
    instead.
+   
+ * Not defining the 6th argument `$format = null` of the
+   `AbstractNormalizer::instantiateObject()` method when overriding it is not
+   supported anymore.
 
 Translation
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