minor #10153 Fixing bad syntax (weaverryan)

This PR was merged into the 3.4 branch.

Discussion
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Fixing bad syntax

Mistake from my PR #10128 :)

Commits
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58898b7 Fixing bad syntax

Author: weaverryan

frontend/encore/installation-no-flex.rst

@@ -1,7 +1,7 @@
 Encore Installation (without Symfony Flex)
 ==========================================
 
-.. tip:
+.. tip::
 
     If your project uses Symfony Flex, read :doc:`/frontend/encore/installation`
     for easier instructions.

frontend/encore/installation.rst

@@ -1,7 +1,7 @@
 Installing Encore (with Symfony Flex)
 =====================================
 
-.. tip:
+.. tip::
 
     If your project does **not** use Symfony Flex, read :doc:`/frontend/encore/installation-no-flex`.