minor #19952 Fix indentation in upgrade_major.rst (karpilin)

This PR was submitted for the 7.1 branch but it was merged into the 5.4 branch instead.

Discussion
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Fix indentation in upgrade_major.rst

Correcting slight indentation issue

Commits
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1911806 Fix indentation in upgrade_major.rst

setup/upgrade_major.rst

@@ -171,8 +171,8 @@ this one. For instance, update it to ``6.0.*`` to upgrade to Symfony 6.0:
       "extra": {
           "symfony": {
               "allow-contrib": false,
-    -       "require": "5.4.*"
-    +       "require": "6.0.*"
+    -         "require": "5.4.*"
+    +         "require": "6.0.*"
           }
       }