minor #19538 [Yaml] update changelog and upgrade files (xabbuh)

This PR was merged into the 3.2-dev branch.

Discussion
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[Yaml] update changelog and upgrade files

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #19504
| License       | MIT
| Doc PR        |

Commits
-------

3cd2932 [Yaml] update changelog and upgrade files

UPGRADE-3.2.md

@@ -75,4 +75,6 @@ Yaml
 ----
 
  * Support for silently ignoring duplicate keys in YAML has been deprecated and
+
+ * Mappings with a colon that is not followed by a space are deprecated and
    will lead to a `ParseException` in Symfony 4.0.

UPGRADE-4.0.md

@@ -147,6 +147,9 @@ Translation
 Yaml
 ----
 
+ * Mappings with a colon that is not followed by a space are are not
+   supported anymore and lead to a `ParseException`.
+
  * Starting an unquoted string with `%` leads to a `ParseException`.
 
  * The `Dumper::setIndentation()` method was removed. Pass the indentation

src/Symfony/Component/Yaml/CHANGELOG.md

@@ -4,6 +4,9 @@ CHANGELOG
 3.2.0
 -----
 
+ * Mappings with a colon that is not followed by a space are deprecated and
+   will lead to a `ParseException` in Symfony 4.0.
+
  * Added support for parsing PHP constants:
 
    ```php