minor #19662 Update version in build.php (AurelienPillevesse)

This PR was merged into the 7.1 branch.

Discussion
----------

Update version in build.php

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/releases for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `7.x` for features of unreleased versions).

-->

Commits
-------

ef3b01d Update build.php

Author: javiereguiluz

_build/build.php

@@ -20,7 +20,7 @@
 
         $outputDir = __DIR__.'/output';
         $buildConfig = (new BuildConfig())
-            ->setSymfonyVersion('7.0')
+            ->setSymfonyVersion('7.1')
             ->setContentDir(__DIR__.'/..')
             ->setOutputDir($outputDir)
             ->setImagesDir(__DIR__.'/output/_images')