minor #12664 #12630 Update .env for "send grid" recipe change (Thomas Berends)

This PR was squashed before being merged into the 4.4 branch (closes #12664).

Discussion
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#12630 Update .env for "send grid" recipe change

Fixes #12630

#SymfonyHackday

Commits
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3dfe2d6 #12630 Update .env for \"send grid\" recipe change

Author: wouterj

mailer.rst

@@ -63,15 +63,14 @@ You'll now have a new line in your ``.env`` file that you can uncomment:
 .. code-block:: bash
 
     # .env
-    SENDGRID_KEY=
-    MAILER_DSN=sendgrid://$SENDGRID_KEY@default
+    MAILER_DSN=sendgrid://KEY@default
 
 The ``MAILER_DSN`` isn't a *real* address: it's a simple format that offloads
 most of the configuration work to mailer. The ``sendgrid`` scheme activates the
 SendGrid provider that you just installed, which knows all about how to deliver
 messages to SendGrid.
 
-The *only* part you need to change is to set ``SENDGRID_KEY`` to your key (in
+The *only* part you need to change is to replace ``KEY`` in the ``MAILER_DSN`` (in
 ``.env`` or ``.env.local``).
 
 Each provider has different environment variables that the Mailer uses to