minor symfony#29033 Fixed typo (KatharinaSt)

This PR was submitted for the master branch but it was merged into the 2.8 branch instead (closes symfony#29033).

Discussion
----------

Fixed typo

| Q             | A
| ------------- | ---
| Branch?       | 2.8 up to 4.1 for bug fixes <!-- see below -->
| Bug fix?      | no
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| 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 -->

<!--
Write a short README entry for your feature/bugfix here (replace this comment block.)
This will help people understand your PR and can be used as a start of the Doc PR.
Additionally:
 - Bug fixes must be submitted against the lowest branch where they apply
   (lowest branches are regularly merged to upper ones so they get the fixes too).
 - Features and deprecations must be submitted against the master branch.
-->

Commits
-------

5bdcda9 Fixed typo

Author: nicolas-grekas

UPGRADE-3.0.md

@@ -681,7 +681,7 @@ UPGRADE FROM 2.x to 3.0
    As a value for the option you must provide the fully-qualified class name (FQCN)
    now as well.
 
- * The `FormIntegrationTestCase` and `FormPerformanceTestCase` classes were moved form the `Symfony\Component\Form\Tests` namespace to the `Symfony\Component\Form\Test` namespace.
+ * The `FormIntegrationTestCase` and `FormPerformanceTestCase` classes were moved from the `Symfony\Component\Form\Tests` namespace to the `Symfony\Component\Form\Test` namespace.
 
  * The constants `ROUND_HALFEVEN`, `ROUND_HALFUP` and `ROUND_HALFDOWN` in class
    `NumberToLocalizedStringTransformer` were renamed to `ROUND_HALF_EVEN`,