minor #9126 Fix environment variable name (pwaring)

This PR was merged into the 4.0 branch.

Discussion
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Fix environment variable name

Typo in environment variable means that it doesn't match other references.

Commits
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6f433da Fix environment variable name

Author: javiereguiluz

quick_tour/the_architecture.rst

@@ -298,7 +298,7 @@ Thanks to a new recipe installed by Flex, look at the ``.env`` file again:
     + DATABASE_URL=mysql://db_user:[email protected]:3306/db_name
     + ###< doctrine/doctrine-bundle ###
 
-The new ``DATBASE_URL`` environment variable was added *automatically* and is already
+The new ``DATABASE_URL`` environment variable was added *automatically* and is already
 referenced by the new ``doctrine.yaml`` configuration file. By combining environment
 variables and Flex, you're using industry best practices without any extra effort.