minor #29400 Add upgrade from 4.2 to 4.3 (ro0NL)

This PR was merged into the 4.3-dev branch.

Discussion
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Add upgrade from 4.2 to 4.3

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #...   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

Forgotten in #28858 i guess. cc @nicolas-grekas

Commits
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ce6ecaf862 Add upgrade from 4.2 to 4.3

Author: nicolas-grekas

Tests/Compiler/ValidateEnvPlaceholdersPassTest.php

@@ -215,7 +215,7 @@ public function testEmptyEnvWhichCannotBeEmptyForScalarNode(): void
      * NOT LEGACY (test exception in 5.0).
      *
      * @group legacy
-     * @expectedDeprecation Setting path "env_extension.scalar_node_not_empty_validated" to an environment variable is deprecated since Symfony 4.2. Remove "cannotBeEmpty()", "validate()" or include a prefix/suffix value instead.
+     * @expectedDeprecation Setting path "env_extension.scalar_node_not_empty_validated" to an environment variable is deprecated since Symfony 4.3. Remove "cannotBeEmpty()", "validate()" or include a prefix/suffix value instead.
      */
     public function testEmptyEnvWhichCannotBeEmptyForScalarNodeWithValidation(): void
     {