minor #16654 [Yaml] sync changelog and upgrade files (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
----------

[Yaml] sync changelog and upgrade files

| Q             | A
| ------------- | ---
| Fixed tickets | #16433
| License       | MIT

Commits
-------

062d707 [Yaml] sync changelog and upgrade files

UPGRADE-2.8.md

@@ -505,3 +505,11 @@ Config
    Additionally, if you have implemented cache validation strategies *using* `isFresh()`
    yourself, you should have a look at the new cache validation system based on
    `ResourceChecker`s.
+
+Yaml
+----
+
+ * Deprecated usage of a colon in an unquoted mapping value
+ * Deprecated usage of `@`, `` ` ``, `|`, and `>` at the beginning of an unquoted string
+ * Deprecated non-escaped \ in double-quoted strings when parsing Yaml
+   ("Foo\Var" is not valid whereas "Foo\\Var" is)

UPGRADE-3.0.md

@@ -1228,6 +1228,11 @@ UPGRADE FROM 2.x to 3.0
 
 ### Yaml
 
+ * Using a colon in an unquoted mapping value leads to a `ParseException`.
+ * Starting an unquoted string with `@`, `` ` ``, `|`, or `>` leads to a `ParseException`.
+ * Deprecated non-escaped \ in double-quoted strings when parsing Yaml
+   ("Foo\Var" is not valid whereas "Foo\\Var" is)
+
  * The ability to pass file names to `Yaml::parse()` has been removed.
 
    Before:

src/Symfony/Component/Yaml/CHANGELOG.md

@@ -4,7 +4,8 @@ CHANGELOG
 2.8.0
 -----
 
- * Deprecated usage of @ and \` at the beginning of an unquoted string
+ * Deprecated usage of a colon in an unquoted mapping value
+ * Deprecated usage of @, \`, | and > at the beginning of an unquoted string
  * Deprecated non-escaped \ in double-quoted strings when parsing Yaml
    ("Foo\Var" is not valid whereas "Foo\\Var" is)